I must confess that back in my younger and dumber days I tried dozens of methods of removing a compression ferrule. At best it is a iffy situation but in 99 out of 100 tries it will introduce many more problems than what it might resolve.
Fortunately there is a much simpler solution to your dilemma.
The compression nuts are all made to an industry standard, therefore you can loosen the compression nut, then remove the angle stop valve but leave the compression nut and compression ferrule in place. Now remove the compression nut and ferrule from your new valve, then slide the new valve in place and tighten it with the original nut.
The trim escutcheon ring is made of a light gage brass sheet metal that is chrome plated. You can use a pair of aviation tin snips to cut the old trim escutcheon away, then you can get a two-piece "split trim escutcheon" that fits around the pipe in two half sections and snaps together for a final fit.