Yikes, my muscle memory would freak out if I had to press multiple keys (or even remap an existing key to a lesser used key) to press a standard and frequently used alpha key.
If fixing the keyboard isn’t an option, I’d much rather buy a cheap, portable keyboard than go with key remapping.
However, if you’re set on this, Keyboard Shortcuts might be the way to go. Similar to how you can type “omw” and have it replace with “On my way!”, you could set one up for typing the letter (eg “eee” = “r” and “EEE” = “R”). Since that’s baked into the keyboard shortcut, you won’t have to muck with permissions and it should work universally.