Tried the remap again, it actually does work. I must've tried another scancode suggestion from another StackOverflow question.
The thing that works is just an RAlt to LAlt remap, which apparently also affects its AltGr-ness. I do wonder if there are cases where one would want the L/R distinction (without it being AltGr), but for now it'll do.
Windows Registry Editor Version 5.00
SharpKeys isn't a background utility by the way, it's purely a convenience tool for setting registry values. It's well worth a go.
I was talking about AHK. SharpKeys doesn't have AltGr listed, nor does it detect Alt presses for scancode detection. But for the above RAlt->LAlt remap it's fine.