You can change the assist by overriding states 190190-190195 just paste those states on character cns file and change the red number with the statedef number of the move you want to be the assist.
OVERRIDE STATES PASTE ON CHARACTER'S CNS:
Spoiler, click to toggle visibilty
;==========================
;==========================
; striker
; ƒXƒgƒ‰ƒCƒJ[—
;==========================
; out screen
; ‰ζ–ΚO‚Φ
[statedef 190190]
type=a
movetype=i
physics=n
anim=40
sprpriority=-2
velset=0,0
ctrl=0
[state 0]
type=nothitby
trigger1=1
value=sca
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=screenbound
trigger1=1
value=0
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=playerpush
trigger1=1
value=0
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=assertspecial
trigger1=pos y<0
flag=noshadow
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
;---
[state 0]
type=afterimagetime
trigger1=!time
time=0
;---
; take off
; —£—¤
[state 0]
type=changeanim
trigger1=anim=40 && animtime=0
value=41 ;; ifelse(vel x=0,41,ifelse(vel x>0,42,43))
[state 0]
type=changeanim
trigger1=(anim=[41,43]) && animtime=0
trigger1=selfanimexist(anim+3)
value=anim+3
[state 0]
type=velset
trigger1=(anim!=40)
x=-28*const(movement.yaccel)
y=-10*const(movement.yaccel)
;---
[state 0]
type=varset
trigger1=1
sysfvar(4)=0
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
;---
[state 0]
type=changestate
triggerall=time>38 && sysfvar(0)>0 && playeridexist(floor(sysfvar(0)))
triggerall=(playerid(floor(sysfvar(0))),var(0)=90900)
;old; trigger1=(screenpos x!=[-60,(playerid(floor(sysfvar(0))),var(3))+60]) || (screenpos y!=[-60,(playerid(floor(sysfvar(0))),var(4))+60])
trigger1=(backedgebodydist<-60) || (frontedgebodydist<-60)
trigger2=time>218 ;; for_safety
value=190191
ctrl=0
;--------------------------
; stand-by (change ok)
; ‘‹@’†
;--------------------------
[statedef 190191]
type=u
movetype=u
;;(a),(i) to be KOed
;;(a),(i) KOƒ|[ƒY‚πζ‚ι
physics=n
velset=0,0
ctrl=0
;---
[state 0]
type=nothitby
trigger1=1
value=sca
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=screenbound
trigger1=1
value=0
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=playerpush
trigger1=1
value=0
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=assertspecial
trigger1=1
flag=invisible
flag2=noshadow
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=afterimagetime
trigger1=!time
time=0
;---
;;[state 0]
;; type=changeanim
;; trigger1=1
;; value=anim
[state 0]
type=posset
trigger1=numpartner
x=(partner,pos x)-3*(partner,facing)
y=(partner,pos y)-3
[state 0]
type=turn
trigger1=numpartner
trigger1=facing!=(partner,facing)
;---
[state 0]
type=lifeadd
trigger1=time>1 && roundstate=2 && numpartner && (time%30=0)
trigger1=life<(partner,life)
value=ifelse(lifemax/1000<1,1,lifemax/1000)
;---
; change
; π‘Φ
[state 0]
type=varset
trigger1=roundstate=2 && numpartner
trigger1=(partner,alive=0 && partner,stateno=5150) || (partner,sysfvar(4)<1)
trigger2=roundstate>2
sysfvar(4)=2
[state 0]
type=changestate
trigger1=time>0 && (sysfvar(4)>0)
value=190193
;---
[state 0]
type=changestate
trigger1=time>158
value=190192
;--------------------------
; stand-by (change / partner assist ok)
; ‘‹@’†
;--------------------------
[statedef 190192]
type=u
movetype=u
physics=n
velset=0,0
ctrl=0
;---
[state 0]
type=nothitby
trigger1=1
value=sca
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=screenbound
trigger1=1
value=0
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=playerpush
trigger1=1
value=0
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=assertspecial
trigger1=1
flag=invisible
flag2=noshadow
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
;---
;;[state 0]
;; type=changeanim
;; trigger1=1
;; value=anim
[state 0]
type=posset
trigger1=numpartner
x=(partner,pos x)-3*(partner,facing)
y=(partner,pos y)-3
[state 0]
type=turn
trigger1=numpartner
trigger1=facing!=(partner,facing)
;---
[state 0]
type=lifeadd
trigger1=roundstate=2 && (time%20=0)
value=ifelse(lifemax/1000<1,1,lifemax/1000)
;---
[state 0] ; 2msg
type=explod
trigger1=!time
anim=0
id=1856861 ;;(##009)
scale=0,0
removetime=0 ;;<- or 1
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
persistent=0
;---
; go-out
; o‚ι
[state 0]
type=varset
trigger1=roundstate=2 && numpartner
trigger1=(partner,alive=0 && partner,stateno=5150) || (partner,sysfvar(4)<1)
;;old; trigger2=(roundstate>2)
sysfvar(4)=2
[state 0]
type=changestate
trigger1=time>0 && sysfvar(4)>0
trigger2=roundstate=2 && numpartner
trigger2=(partner,sysfvar(4)=101)
trigger3=(roundstate>2)
value=190193
ctrl=0
;--------------------------
; out (190193-190195)
; “oκ
;--------------------------
[statedef 190193]
type=u
movetype=u
physics=n
sprpriority=-2
velset=0,0
ctrl=0
;---
[state 0] ; 2msg
type=explod
trigger1=!time && sysfvar(4)<1
anim=0
id=1856862 ;;(##010)
scale=0,0
removetime=0 ;;<- or 1
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
persistent=0
;---
[state 0]
type=nothitby
trigger1=1
value=sca
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=screenbound
trigger1=1
value=0
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=playerpush
trigger1=1
value=0
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=assertspecial
trigger1=1
flag=invisible
flag2=noshadow
ignorehitpause=1
supermovetime=-1
pausemovetime=-1
[state 0]
type=turn
trigger1=facing!=(partner,facing)
trigger1=(!time && roundstate=2) || (roundstate>2)
; bind to partner
; ƒvƒ[ƒ„‚Ι‡‚ν‚Ή
[state 0]
type=posset
trigger1=!time && roundstate=2
x= (partner,pos x)+(partner,backedgebodydist+90)*(-facing)
y=-(partner,screenpos y)-10 ;;(-180)
[state 0]
type=posset
trigger1=roundstate>2
x= (partner,pos x)-win*facing*40
y=-(partner,screenpos y)-80 ;;(-280)
[state 0]
type=velset
trigger1=roundstate=2 && !time
trigger2=roundstate>2 && time>(!win)*100
x=abs(pos x-partner,pos x)*0.1*const(movement.yaccel)*(roundstate=2)
y=abs(pos y)*0.1*const(movement.yaccel)
[state 0]
type=changestate
trigger1=roundstate=2 && !time
trigger2=roundstate>2 && time>(!win)*100
value=ifelse(sysfvar(4)>0, 190194, 190196)
ctrl=0
;--------------------------
; empty states for override
; ƒXƒgƒ‰ƒCƒJ[o» γ‘‚«—p’†ΤƒXƒe[ƒg
;--------------------------
[statedef 190196]
type=u
movetype=u
ctrl=0
[state 0]
type=changestate
trigger1=!time
value=190194
ctrl=0
;--------------------------
; striker call / summon
; ƒXƒgƒ‰ƒCƒJ[Ά«
;--------------------------
[statedef 190194]
type=a
movetype=u
physics=n
anim=ifelse(selfanimexist(44),44,41)
sprpriority=-2
ctrl=0
; mark : "p-1" / "p-2" / "cpu"
[state 0]
type=explod
trigger1=!time && roundstate=2 && !numexplod(296000) && numpartner
id=296000
;v1.0; anim=f296000+(partner,ailevel=0)*teamside
anim=f296000+(matchno<2||ishometeam=0)*teamside
sprpriority=5
postype=p1
;old; pos=floor(const(size.head.pos.x)*const(size.xscale)),floor(const(size.head.pos.y)*const(size.yscale)*1.2)
pos=0,floor( (const(size.head.pos.y)-const(size.ground.front)/2-const(size.ground.back)/2) )
facing=ifelse(facing=1,1,-1)
scale=0.5,0.5
bindtime=-1
;op; removetime=80
supermovetime=-1
pausemovetime=-1
ignorehitpause=1
;op; removeongethit=1
persistent=0
;---
[state 0]
type=nothitby
trigger1=1
value=sca
ignorehitpause=1
[state 0]
type=assertspecial
trigger1=1
flag=noshadow
ignorehitpause=1
[state 0]
type=screenbound
trigger1=1
value=0
ignorehitpause=1
[state 0]
type=playerpush
trigger1=1
value=0
ignorehitpause=1
;---
; land
[state 0]
type=changestate
trigger1=(pos y>=0) || ((vel y>0) && (pos y+vel y>=0))
value=190195
ctrl=0
;--------------------------
; land>roundover
; ’…’n>ƒ‰ƒEƒ“ƒhI—Ή
;--------------------------
[statedef 190195]
type=s
movetype=i
physics=s
anim=47
sprpriority=-2
velset=0,0
ctrl=0
;---
[state 0]
type=nothitby
trigger1=1
value=sca
time=8 ;;<-options
[state 0]
type=screenbound
trigger1=1
value=0
[state 0]
type=playerpush
trigger1=1
value=0
[state 0]
type=posset
trigger1=!time
y=0
;---
;---
; goto striker state num *see [state195900]
; w’θstate‚Φ *[state195900]QΖ
[state 0]
type=changestate
trigger1=(animtime=0) && (roundstate=2) && (sysfvar(4)<1)
value=ifelse(var(59)>=200,var(59),1000)
;def; value=1000 ;;<-the 1st sp
ctrl=0
; for ex-change (for safety)
; π‘Φ—p
[state 0]
type=changestate
trigger1=animtime=0
value=0
ctrl=1