porymap VS pokecrystal-speedchoice

If you don't want to code, Porymap is an incredible tool for making custom maps and changing Pokemon encounters.

Seems doable, yeah, especially if you have at least basic C knowledge. If you get the build tools set up, there's already some follower code available, so you wouldn't even have to re-engineer that yourself. And PoryMap can probably handle a lot of the basic edits you want to make.

You can look at the pokeemerald decomp. Instead of using binary tools like Adcance Map and HMA you are editing the source code with a simple text editor and porymap. The pokeemerald has everything up to gen8 (mons, moves, abilities). An example hack that was made with the decomp is Inclement Emerald.

Porymap is the best gen 3 map editor tool, but like the other replies imply it's for decomp hacking only.

decomp has an equivalent to advance map called porymap. it's really not all that different to use. i checked your post history and you mention having trouble with adding new tiles in advance map, i can say from personal experience that adding new tiles in porymap is very easy.

the other option i can think of is the pokemon emerald decomp. you would have to learn a bit to get a decomp working, then use pokeemerald-expansion's pokemon_expansion branch as a base. once you have that decomp set up you could just use porymap to change wild pokemon locations and make those pokemon available in the wild.

porymap!

you actually don't need to build it yourself! there is a release page with the most up-to-date version as an ips patch file.

that would be the speedchoice rom! download the ips patch file from this page, and use the program lunar ips to patch it to a clean unmodified crystal rom.