Sometimes those schreader valves don't seal up when you remove something after its been connected a while (like when you use a quick coupler on an old ac system). I think i'd plan on recovering the refrigerant. You may want to have a 1/4" copper washer to hand incase one is fitted between the hp switch and the schreader.
You can set up the switching pressures of the new hp switch using nitrogen and your gauges before fitting it.

Cheers Jon