I found a solution to this, at least the hotkey part, but it's not universal. It requires editing each emulator's retroarch.cfg file separately. (Of course that means it only works for the emulators that use LibRetro.) This solution is the same as this one.
The ultimate answer is "YES."
As I mentioned, I have some special reasons for wanting to do this, but if you don't enable a hotkey, then there's a problem because the Player1Start button is used for both starting a game and exiting the emulator. Even if you're not a power user, there are other functions that work only with the hotkey feature. So, at first glance, it seems like there's no way to avoid using a hotkey.
I've eliminated the hotkey in Mame-Libretro as well as in EmulationStation, which will help with some groups of friends that will be at my gaming gatherings in the future. (I figure at some point the pandemic will reach a point where we can gather in groups again - at least small groups.)
I'm not using a normal gaming controller. I'm using an Emulator Edition Plus console as part of an arcade cabinet:
Note the extra white A & B buttons on the top left, as well as extra white A2 & B2 buttons, also at the top on the left side of center. Then, to the right, there's a Navigation Menu with 10 keys, Left Mouse Button, Menu, Pause, Exit, and Right Mouse Button along the top. The next row is StartPlayer1, Coin, Select, Coin2, and StartPlayer2.
I also have a door under the console that opens up for a keyboard shelf. It took me a while to realize that I can put power functions on the keyboard so guests don't use them and mess things up.
So here's what I did:
I went into the RGUI and used it to change /opt/retropie/configs/mame-libretro/retroarch.cfg. Under Settings->Input->Hotkey Binds, I changed Exit to the Exit button, Pause to the Pause button, and Reset to the Menu button. (I figured that when you hit Menu to reset the game, you're going to the game's "Menu.") For a bonus, I changed Left Mouse Button to Slow toggle and the Right Mouse Button to Fast forward. I changed Toggle Menu to F1, which is not reachable or useable from the console panel. I also used the A & B buttons on the left to increment and decrement the save state slots and used the A2 & B2 buttons to save and load states.
There's other functions I don't necessarily want people using that I figure I can bind to keys on the keyboard and not to controls on the console.
I tested everything out to make sure I had set up the right bindings in the first place. At this point I had to use Select (my hotkey) to make it work. But then, as a test, I went in and undefined the hotkey. I saved the config (again, to /opt/retropie/configs/mame-libretro/retroarch.cfg), then tested it.
Everything worked fine. So now I can pause by just hitting Pause, without a hotkey. The same with Exit and other functions that previously required a hotkey.
The trick is to redefine all the function bindings and bind them to buttons or keys that are not used without the hotkey first. Once those functions are moved to other keys or buttons, then you can remove the hotkey definition.
