Will extending my 90-day Non-O visa to a year invalidate my re-entry permit for Cambodia?

I will say a friend of mine had a yearly extension and a re-entry permit, he went and got a new extension but didn't get a re-entry. The immigration office said he could use the old re-entry permit as long as he got back before it expired (nothing to do with the extension) and when he came back he was stamped in on the new extension using the old re-entry permit

SO I would imagine it'd be the same for you, as long as you get back in to the country before that re-entry permit expires it'd work.

Seeing as you're getting a yearly extension before you leave ASK THEM while you're there, the last thing you wanna do is lose the Non-O visa/extension just because you didn't buy a new 1000baht single re-entry permit

good question, I would ask the immigration office when you get the year extension.

I would imagine that as long as you return BEFORE the re-entry permit expires you'll get stamped in on year extension when you come back.