Looking for tips from someone who has replaced the trim locks on a NP wave boom.

I think I need to replace the old barrel part with the new one due to the design of the clip part?

If so, what's the best way to get the old barrel part off the boom? Seems solidly stuck on, not wanting to budge.

Any tips would be appreciated.

All good, I worked it out. No need to take the barrel off. Put the clip in some hot water for a few mins and then clips on reasonably easily.

Glad you fixed it!
If someone else is looking...I recently regripped an old NP RS:X boom. Used the open claws of an adjustable wrench on either side of the barrel, and gently tapped the wrench with a mallet. The barrels came off quite easily, and appeared just to be pressure fit (no glue).
There's a good video by Severne on Vimeo called Boom Re-Grip that shows the technique.