Redoing bathroom plumbing

I'm painting, updating my old bathroom. House is circa 1925.

The sink drain goes into a chrome slip fit nut, then into a P-trap that has what looks like a socket fitting that joins what I call a spud tube with built in bell that mates the wall. It is all chromed, with some pitting.

How are those pieces attached? I'm assuming the spud is threaded onto a nipple or into a coupling in the wall and the trap part is sweated to the spud. What's the trick to getting that out? Odds that it will happen leaving useable threads?

The supply lines for the toilet and sink come up via long chrome nipples. Basically I have the same question; what are the odds the nipple will come out leaving useable threads? Tips?

Thanks

P traps are connected to drains with a slip joint into a threaded nipple that in turn goes into a tee. Considering the age of the house, the drain is very likely galvanized pipe and the nipple may be badly rusted on the end especially. The chrome pipes in the floor also a galvanized pipe and I would not consider them to be worth saving. They screw into pipes under the floor or in the wall. The hard thing about working on plumbing in an old house with galvanized pipe is finding a place to quit replacing pipe. Ideally, the whole house should be re piped, but that most likely far beyond what is in the budget for the bathroom renovation.