I disagree with the second part. You have to be employed full time while you are applying for a PNP and waiting for the nomination. Once you receive your nomination you can change your job. Once again if you do not have any restrictionsAssuming that OP was holding a Post Graduate Work Permit but applied under BC PNP international graduate stream with job offer, then changed his/her job before getting, then they must inform BC PNP abut job change otherwise their nomination will be withdrawn.
But yes, only those PNP without employment restrictions can change their job but their conditions must be the same as they were nominated.