My understanding is: Yes. You get the GC for 5 years of service in an underserved location and once you have submitted your evidence of 5 years of full-time practice you are free to work the night shift at the 7-11 with your EAD.
However, as there is no clear guidance on this issue from USCIS (as there is no clear guidance on about 99% of what they expect us to do), there are conflicting recommendations from various immigration attorneys on the wisdom of this strategy.
I cannot give you legal advice on this. I am a very risk-averse person and would consider to stick it out for another 6 months until you have that plastic card in your hands. But thats just me.
There are other people on this board who have gone through exactly your scenario (going for fellowship after 5 years), they would be able to give you better information.