There is a noise in the rear cv joint or universal.  The cv joint has been replaced but the noise persists so I suspect it is the universal.  The universal is crimped.  Can I replace the universal joint if I undo the crimping or do I need a new shaft

I'm sure you can replace the uni-joint on your tailshaft... but I'm not an expert in that area and would be asking a driveline shop for advice to be 100%.

The technical term is staked.
Can't be easily replaced.

Can grind them out.
Most people tack weld em back in.

There is a prop shaft repair shop here in Western Australia that does the staked joints, I recently had one done on a bmw sedan and when looking at the replacement it had been restaked ,they must have the machine to do it