; this will install a custom sprite in sprite slot 36, you can make it support other null slots though.
; for the tweaker shit, you know the drill. set it as in the .cfg
; you can even replace normal sprites with this method, not sure why would u tho.

;step 1: use freespace IN BANK 1 to setup a handler

org $01E2B0
;init handler
InitCustom:
    JSL InitHandler
    RTS

MainCustom:
    autoclean JSL MainHandler
    RTS

;step 2: point to the handlers
org $0181E9
    dw InitCustom
org $018638
    dw MainCustom

freecode
InitHandler:
    PHB
    PHK
    PLB
    LDA $9E,x
    CMP #$36
    BNE +
    JSR InitVenus
+   PLB
    RTL

MainHandler:
    PHB
    PHK
    PLB
    LDA $9E,x
    CMP #$36
    BNE +
    JSR MainVenus
+   PLB
RTL

InitVenus:
;init code of the sprite goes here

MainVenus:
;main code of the sprite goes here