I've seen someone do this, upgrade their account to founders through a retail code, and it is certainly possible, but a legitimate code is very hard to come by. What you cannot do is purchase anything above the Standard Edition founders pack, so anything claiming it has a valid code for the Ultimate Edition or something like that is a bs scam. That founder status is then automatically upgraded to founder level 2 because that was a thing Epic did with the founders accounts.

In fact it is true that if you had a legitimate code, you could certainly make yourself a base, Standard Edition founder.