Wait, you can't use the cheat functionality of something like RA for individual Widescreen support in games!?
Reicast in Retroarch lakka lacks cheat support.
Reicast (Alpha) has a "widescreen" option (same as in lakka), that basically is "generic widescreen cheat", but that doesnt work as well - as individual cheats/hex editing games. Because people who found out codes for the individual games, also looked into stuff like clipping fixes, and sometimes moving some GUI elements slightly, to have them centered on screen again.
There is basically a 70 page thread, thats linked in here several times already, that has all that stuff in it already. They started out "cheatcode centric", but eventually moved into hex editing the games themselves. Its basically the same stuff. Instead of ram hacking (cheatcodes), you write the modifications to the .gdi itself.
As Reicast (Alpha) also doesnt have a cheat option, and people havent reporterd codebreaker, or gameshark working (I didnt even try to be honest - both of those where "bootdisks", that sometimes also work in emulators.), hex editing is where its at.
The 70 page thread with all that stuff in it also kind of turned into that direction. People universally came to think of hexediting existing games as the "best option". (Because it also works on real hardware - and removes steps (like booting gameshark first).
Works great, just takes time. Much less time, than compressing the .gdi's though. If you are reasonably fast navigating on your PC...