I actually wasn't thinking correctly. The R4 doesn't reinitialize the filesystem after reinsertion, so you won't be able to use Eepinator to dump save files, but if all you're doing is restoring a save file to an original cart, Eepinator should work fine. This will probably be easier than the other two options, which both require Wifi to connect to your computer.
I've never used Eepinator myself so I don't have detailed instructions for you, but I'd imagine that you'd load the program, select the *.sav file to transfer, then swap carts and let it put the save file onto the original cartridge.