lorom

org $8Fxxxx   ;free space in bank $8F; offset 7xxxx 
PHP            
SEP #$20       

LDA #$00      ;load red scroll to... 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 

LDA #$01      ;load blue scroll to... 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 

LDA #$02      ;load green scroll to... 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 
STA $7ECDxx   ;screen xx-20 

PLP           ;End of door scroll ASM 
RTS           ;End of door scroll ASM

;so for screen $04, you'd have STA $7ECD24
;for screen $1A, you'd have STA $7ECD3A

;comment (add ; at the start) of any lines you don't need, and save this file as a copy (leaving the template untouched) with the same name as your rom.