First, you need to physically expand the rom.
Duplicate the first 128k after the NES header, then change the header to indicate that the PRG size is now $10 instead of $08.

Then make these changes to allow the game to use the expansion:


Paste this code into FF64 (3FF74)
	A9 00     LDA #$00
	8D FE 7F  STA $7FFE
	8D FF 7F  STA $7FFF
	4C 70 FF  JMP $FF70

Modify reset vector at FFFC (4000C)
 replace this:
  70 FF
 with this:
  74 FF


Paste this code into FF4C (3FF4C)
	4A        LSR
	4A        LSR
	48        PHA
	29 08     AND #$08
	8D FE 7F  STA $7FFE
	68        PLA
	29 07     AND #$07
	60        RTS

Go to CBA6 (3CBB6)
 Replce this:
  4A        LSR
  4A        LSR
  29 07     AND #$07
 With this:
  20 4C FF  JSR $FF4C
  EA        NOP

Paste this code into FF58 (3FF68)
	8D 69 07  STA $0769 
	48        PHA
	AD FE 7F  LDA $7FFE 
	8D FF 7F  STA $7FFF 
	68        PLA
	60        RTS

Go to CD59 (3CD69)
 Replace this:
  8D 69 07  STA $0769
 with this:
  20 58 FF  JSR $FF58

Replace the bankswitching code at FFC5 (3FFD5) with this:
	A9 00     LDA #$00
	F0 06     BEQ $FFCF
	AD 69 07  LDA $0769
	0D FF 7F  ORA $7FFF
	8D 00 E0  STA $E000
	4A        LSR
	8D 00 E0  STA $E000
	4A        LSR
	8D 00 E0  STA $E000
	4A        LSR
	8D 00 E0  STA $E000
	4A        LSR
	8D 00 E0  STA $E000
	60        RTS