Hey John.

Yes 80% or more face coverage is compulsory for the passport size photo you are required to upload for NEET applicaion.and Yes, the same is given in the released brochure as well

Not following th guidelines might lead to rejection of your application . But, you can edit your application from January 15, 2020 if you have made any mistake of any sort while filling the application.

hope this helped.

all the best.