wrote

I have an overhead light fixture with 3 40 watt bulbs. one of them
burnt out. can I replace only the burnt out bulb with an LED bulb?

Yes.

What if any would be the consequinces?

It wouldnt look that great. Better to replace them all with a led bulb.

But if you have it on a dimmer, it may not
dim well unless you replace the dimmer too.

Thanks for a reply

Even one that tells you to shove your head up a dead bear's arse ?