MAC bases
MAC has lots of different base locations, mostly along the eastern seabord. Some will change from time to time, but most of them are fairly long-term. Fedex decides when and where an ATR will be placed: MAC has no say in it, other than to ask "how high?" on the way up!
Currently, the places MAC has ATRs based are BQN (forget about it - you couldn't pry the pilots there out with a crowbar!), CHA, EWN, DHN, DLH, ILM, IND (hub), MEM (hub), MIA, and MYR. It is not very common for a pilot to leave an established run. Usually openings come for new base locations, when a FO moves to the right seat, or those rare occasions when a pilot leaves the company.
Currently, no ATRs are based in GSO: the EWN and ILM planes do an "overnight" turn there. Flight crews bid for locations when they open up: you'll "float" for a while after you new-hire. There may be an ATR based in GSO when Fedex increases its operations there, but there are already several Captains and FOs who have expressed an interest in bidding for that run, if and when.