The .srm file is a representation of the game's SRAM memory the emulator keeps for when it's no longer running, just like real SNES cartridges are battery powered to preserve the save.
I guess one way to do it is to follow the tutorial for adding an intro, but instead of all the graphical programming to display an intro screen, it instead just:
- Checks if the game's SRAM is empty or not, in other terms if you played the game for the first time or not. If it's not empty it skips the rest of the programming. This is in fact needed unless you want the game to erase any progress made on future playthroughs whenever it's booted and returning it to that initial state.
- Copy 64kb (or whatever size the game's SRAM is) from the ROM, from an address where you hex edited in the contents of your *.srm file with the mid-game save, to the SRAM.
- Continues to the original entry point of the ROM that launches the game as normal.
And yes, you'll need to know ASM to write that program. It's fortunately simple enough, in fact the method could be repurposed for other games, providing there is space for the .srm file in the ROM.