but, for build a room(no chip) the "only" assembly modifications that could be made would be the adresses of the diferent mappers, or not? what moooore would be?
NESmaker uses mapper 30 (UNROM512) by default. It provides 512KB of PRG-ROM divided into 16KB banks, and 4x8KB CHR-RAM banks.
For better or for worse, the software and codebase are built around this mapper. Changing it to use another mapper let alone one with expansion audio would require major changes.
First major change: CHR-RAM -> CHR-ROM
CHR-RAM means that tiles are manually written to the PPU (graphics processor). It allows for graphics to be stored (even compressed) onto PRG-ROM.
CHR-ROM means that tile data is stored into a separate chip on the cartridge, directly connected to the PPU. Most mappers with expansion audio use CHR-ROM banks, so the codebase would have to change to account for it. (The FDS is its own nightmare to code for)
Second major change: PRG-ROM bank size
A few mappers with expansion audio support 512KB of PRG-ROM (exceptions: MMC5 is 1024KB, Sunsoft 5B is 256K), but the size of the banks are usually 32KB, 16KB or 8KB. The codebase & bank structure would have to change to account for this.
Third major change: Register layout
This has already been mentioned by Ne0. Changing mappers always involves changing the codebase to use the correct mapper registers. You could make a system to automagically set them up, but you'd need to be working with a variety of mappers to justify that.
Honorable mention: FC vs NES
Only the original Famicom can play expansion audio without modifications to the console. Enabling expansion audio on the NES involves adding circuitry to the expansion port on the underside of the console. This isn't an issue on emulators, but you may want to consider making the music in such a way that the lack of expansion audio doesn't ruin the compositions on an unmodified NES.
You also need to keep in mind that NESmaker becomes less and less useful with each modification to the codebase. At some point you will realize that it's easier to bypass the software and make/use a different toolchain for NES development. A few members here have become aware of that fact already.