Shut of valve replacement guidance

Hi, I am rather new to the plumbing scene for DIY work, and I could use a bit of advice. I am working on a secondary bathroom that has been neglected for years. Eventually I am going to remodel it but for the time being I just want to replace the toilet. So the shut of valve is stuck in the open position and it looks like a piece of junk to begin with. I have already tried to unstick the valve with some liquid grease. However, that didn't work. From some reading I have done the best option seems to be just to replace it. At first I thought I was dealing with a sweated on shut off valve. However, the tube which it is attached to is chrome not copper. From what I can tell the thing is one piece. I pulled back the flashing where the pipe joins the wall and I think this thing is sweated on. On the underneath of the pipe I believe I see a solder bead. Though I could be wrong as I saw some other folks who have had pipes that screwed on. yet I see no threads or evidence of any plumber tape. As I am new to this I would like someone else's opinion that is not as green as I. So my plan is to sweat the pipe off and replace the existing end with a compression valve if there is enough pipe hiding under the existing one. Though I guess I wont be sure until I get the pipe removed then I can see what I have to work with. I am guessing there wont be more than an inch that is hiding under the other pipe. I guess I might end up having to replace what is there with something similar.... Thanks in advance for any advice. Kevin