I'm hacking a 'LoROM' game at the moment (Super Metroid). I think I understand mappers pretty well at this point, and I understand what LoROM means and what it doesn't mean. That's not what I need clarification of.
Someone mentioned LoROM usually uses $[70-7f|f0-ff]:[0000-7fff] to access SRAM. Anomie's memory map mentions that F0-FF can read and write at a higher speed with the appropriate bit set.
So, my questions are: Can I switch the game to use those addresses for faster SRAM access and maybe even as expanded RAM? And how do emulators / flash carts decide how to map or mirror the sram addresses?

Banks $80-$ff can be read at 'FastROM' speeds. Sure, you could theoretically relocate almost anything you want on a cart anywhere. The SNES doesn't care what's at the other end of the address bus. It won't be 'LoROM' anymore though, it would be custom cart using a custom mapping and I don't think any emulator would support it anymore.

I don't see what purpose faster SRAM access speed would do though. What are you trying to accomplish? Speeding up saving and loading in a game?

Emulators either have an internal database, read the internal information int the ROM or perform other testing to determine what type of mapping it is. Copiers read the copier headers when they load a game that tell them what type of mapping it should do.

If you had no copier header, the copier wouldn't know what to do with the ROM unless you told it.

If you make up some new cart layout, it's likely no emulator or copier would support it.

I'm planning on adding something that requires a large amount of contiguous RAM, and the original game doesn't really have that sort of space lying around. And faster speeds for free would be nice.
I've been poking around a bit though, and emulators seem to disagree about mirroring SRAM in F0-FF for LoRom and I'm not sure about copiers either, so I'll probably just use 70 regardless.