Unless you have the original "square rim tips" on the exhaust tips, consider and weigh the benefits of spending money and time on labor and tools and just buy a new set of tips with the rounded rolled edges.
This is also why stainless steel makes good sense on an old classic that is going to be around for a while.
That being said, there are tools such as air chisels and pipe expanders that can help you. There are also inductive heaters to place around the outside chrome, or gentle heat from an industrial heat gun (not your wife's hair dryer). You may be able to "break that bond" between the chrome tip and the underlying steel exhaust tip and be able to eventually twist it off. The challenge is not damaging the chrome. A little discoloration from heat can always be polished out.
If you do replace the system with an OEM and non-stainless, consider the old trick of cutting a slot in the steel tip of the muffler; this will facilitate the next time you need to do this.