I'm a rivet guy... me likey rivets Others have welded the rivet heads (I think that's what you mean?) with no issues, so I don't think there will be any long-term issues with that. It is .223 after all!
If I'm understanding correctly then internally the rivet is still doing its job... you just gave it a different head. It's .223 so I doubt there will be much stress vs. a .30 cal. Should be fine. If not you can easily re-repair it with another weld!
I like the rivets too! Nothing more appealing than the “bumpy side” of a 240B. AK’s look fine with rivets PLUS I think there is something to the welds on non-tempered flats. Just my opinion.