the tail piece is spot welded in place. any reputable place can deal with it no problem. I wouldnt waste time with a cut/patch on that section but thats me. Its not big flat area. Its smaller area with quite a bit of curve to it.
but really do what you want. Youll have a hundred opinions on what route to go.
I just dealt with that exact area and if wasnt bad(not from the underside. theres no guarantee it is you have to see when you start to take it apart and clean it up) it could be fixed easily. If its gone through id replace the whole tail piece.
heres an e36 with it removed and new one installed.
what Ive learned is also to use the oem paint code with real paint. best results everytime.