You are going to need a more complex code to support more than one slot in this is the case and if there is no alternative on the emu.
Did you tried to ask on the emu forums/git if there is any other way to choose the slot to save or to start from a fixed slot?
As the emu is still under development, maybe they could help you on that.
Anyway, if that is not possible, you are going to need to create a code on the module, under the Save state slot label, that reads from a module setting the current saved slot, saves the game and update the current saved slot once it is done saving.
This would only work if you only use RL to save your games, as the current selected slot info would be loose if you don't.
A much more complex code could try to parse the current slot info given from the emu on the screen, but this would require some more knowledge on AHK codding.
If you want to try the RL module label way, I wrote about two or three weeks ago a post about using the save and load state labels under more complex save cases (where simple fixed key presses are not enough for the emu).
Just try to search for it if you want to know a little bit more about it and make any questions you want and I will try to help you on the process.
Edit: by the way, thank you very much for sharing this!!!
Please keep doing it as it is a huge contribution for us.
Also, if you simply add to the list the emus that out are able to make work with the default emu config, the ones that need some special configurations and the ones that you can't add support for the save and load state features we would appreciate a lot.
I promise you that whenever I can I will try to add support for any problematic emus to improve your list!!!
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