I'm remodeling my son's bathroom and the old copper lines have compression fittings for the shut-off valves.  I want to install new valves.  After a loosen the nuts the sleeves will not move when I pull on the nuts.  I do not want to cut the the sleeves and nuts off because then I will have to sweat on an extensions.  Do you have any plumber tips for me?  Can I put on a new valve and use the old sleeve and nut?

Danl

No doubt the copper has compressed to the sleeve.  I’d take a little steel wool and buff the sleeves and try a new valve.

The compression ferrule should be reusable if it isn’t damaged and was installed at the same point as required by the replacement valve. 
Ron’s suggestion about the steel wool is a good one 

Clean it up best you can and put the new valve on, don't over tighten.  Snug it up and try it.  If it leaks a little, turn the water off and tighten a little more.

If all else fails there are relatively inexpensive tools that pull them off. Here's one, though I suspect there are some at a local box store. Be aware that if you choose to remove it, the surface of the pipe may be scarred enough that making a new one fit and not leak might be a challenge.

Edited November 1, 20223 yr by Fred W. Hargis Jr

Thank you all for the quick response and great advise.  I will give your suggestions a try.  Thanks again, I appreciate it.  

Danl