You have to get to the back of the valve to disconnect it from the water supply and to reconnect the new valve. You don't show enough of the area around the valve to see how much work it will be to get the surrounding material free, but it is ABS and it should not break if you are careful. On the Minuet, the shower valve was in a housing with aluminum trim pop riveted in above and below to hold it in. Remove the pop rivets and the aluminum trim and the valve back side was exposed as the surround came out. Fight some corrosion around the nuts that mount the valve and around the water connections and take the valve out. When you replace the valve and connect it up, pay attention to how you put the fittings as the surround has to fit over the assembly. It's not difficult, just a little time consuming.
1978 Argosy 6 Metre Minuet
2006 Toyota Tacoma