re-attach old skimmed board or replace?

[redhexagonal]

I unscrewed this bit of plasterboard above a door so I could shim out the studs and straighten the board up. I managed to get it off in one piece without cracking it. Can I get away with screwing it back on or should I use a fresh piece of plasterboard? I have never skimmed so I thought I could get away with easifilling the holes and edges on the old board. Otherwise its a job for a plasterer unless I can work out how to skim....

 

[RandomGrinch]

I would attach a new piece of plasterboard.
No need to skim though, just fill the screw holes with easyfill and use a flexible/hybrid sealant around the edges.