I think guards in prison should have the perms to be able to fix prefix glitches. I see these all the time, and I think the guards could definitely help reduce the glitch. Maybe the player must show proof to the guard with something like a screenshot of what their old rank was before donating.
Let me tell you now, if I had /pex, I would screw everything up in three seconds. I admire the idea, but I think it would be better if it would be applied to Head-Guard first, not Guard.