ROM Hacking NES with FCEUX

[Saturn]

A quick and easy how-to for rom hacks with FCEUX (and assuming it's already installed/configured)

This goes hand in hand with the NES 'Game Code Modifications' :p thread.

Open FCEUX and load a rom. For this example, I'm using Die Hard (U)
Discover Game Genie Codes on your own or go to this page to pick from them.
Compile a list of what you want, need or have (sometimes limited) access to. Here are my picks:

Infinite shots on all guns:
ATVEIZSZ

Infinite Time:
SXKYZPVG
SXKNYPVG

Invincibility:
AAXAPASZ

Radio Worth All Items:
NYNXULAO

In FCEUX, click Debug-Game Genie Encoder/Decoder
Paste in one of the codes from the list into the field on the left of the dialog box under Game Genie Code
To hack the rom itself, double click the address that auto appears under Possible Affected Rom File Addresses at the bottom of the dialog box.
The value will open with the first byte highlighted in FCEUX's built in Hex Editor
This value will be the same as the Compare value in the Game Genie Encoder/Decoder dialog box.
Change it to the value in the Value field of the Game Genie Encoder/Decoder dialog box by simply typing the new characters (when the Hex Editor window is in view)
To save and consequently, modify the rom with the new hack, there are 3 useful ways:
    1. In the built in Hex Editor window, after making changes click File-Save Rom. The changes will be made to the original rom immediately.
    2. (Recommended) In the built in Hex Editor window, after making changes click File-Save Rom As... This will open another window allowing you to rename the rom something else (for testing purposes or to keep both or to keep the original intact or whatever)
    3. Highlight and copy the string of bytes around the area to be modified and open the rom with another hex editing program. Then, paste the searchable into the Find box to ensure it's searchable/usable and post online for everyone else who wants to do the same thing... like this

So, for Infinite shots on all guns, use Game Genie code ATVEIZSZ
Open in a Hex Editor
Search: 199D3506A52CF00585682098C6A5
Change: 199D3506A52CF00585682098C660
1 instance

Infinite Time 1 of 2: SXKYZPVG
Search: F064C6AF1060A9018D8A
Change: F064A5AF1060A9018D8A
1 instance

Infinite Time 2 of 2: SXKNYPVG
Search: A9018D8A07A93B85AFC6
Change: A9018D8A07A93B85AFA5
1 instance

Invincibility: AAXAPASZ
Search: A8A5A5D022A5A8D00620A0
Change: A800A5D022A5A8D00620A0
1 instance

Radio Worth All Items: NYNXULAO
Search: 790920857960AD79070910
Change: 790920857960AD790709FF

Load up the new rom in most any emulator and it works like a charm. Personally, this is the only reason I use Windows anymore. Seems there's not adequate hacking tools to match this ease of use in Linux yet so I hack em in Win 7 and play em in Lubuntu

[zapiy]

I am going to give this a try chap..

[Saturn]

Awesome. The method above is a cinch. Creating your OWN Game Genie codes is a little harder but worth it some cases. A lot of custom GG codes are crap but some are useful. I've loaded up more games to add. Just need time to do 'em. Good luck