Not possible as saves are stored on the console not the cartridge.
You could use an unbanned modded switch, transfer the save to it, pull it off the modded switch, mod it, then put it back. I've done that no problem. But that requires a second switch which is obviously cost prohibitive.
Edit: Actually thinking more about it, if your Switch is moddable but you just don't want to, you may be able to dump the save data using TegraExplorer. It's like GodMode9 on a 3DS. Still requires a moddable switch and a way to get into RCM but jigs are extremely easy to 3D print or buy. I don't know if you can reinject the save or if you can dump it but it's an avenue to explore. You'd theoretically have full access so I can't see why you shouldn't be able to dump it and decrypt it with some kind of PC tool and your device keys (which you can also dump with TegraExplorer)
Not possible as saves are stored on the console not the cartridge. You could use an unbanned modded switch, transfer the save to it, pull it off the modded switch, mod it, then put it back. I've done that no problem. But that requires a second switch which is obviously cost prohibitive. Edit: Actually thinking more about it, if your Switch is moddable but you just don't want to, you may be able to dump the save data using TegraExplorer. It's like GodMode9 on a 3DS. Still requires a moddable switch and a way to get into RCM but jigs are extremely easy to 3D print or buy. I don't know if you can reinject the save or if you can dump it but it's an avenue to explore. You'd theoretically have full access so I can't see why you shouldn't be able to dump it and decrypt it with some kind of PC tool and your device keys (which you can also dump with TegraExplorer)