Even if HeartGold is out, I still anticipate this hack a bit. It looks pretty solid and it seems like a lot of work has already been put into it.
I've never heard of unLZ-GBA hacked, but umm, unLZ-GBA itself is extremely outdated. GBA Graphics Editor can do everything unLZ-GBA does and much more. It's also more efficient and can be run on non-Windows operating systems with Mono installed.
I would give you a link but I'd probably be banned or posting links to other websites... to give you an idea, it can load palettes (compressed and uncompressed), graphics (LZ77 compressed and uncompressed), TSA, edit colors, view 4bpp, 8pp, indexed bitmap and truecolor bitmap graphics (IIRC), insert bitmaps with multiple options (abort options, repoint graphics and/or palette), save bitmaps, load TSA/view an image with TSA loaded, and yeah.
IPS patching works too but UPS patching is better IMO. NUPS is the best program for UPS patching but Tsukiyomi works too.
Just some suggestions to try and help a little. Good luck with the hack.