When a community lot contains one or more rabbitholes, the purpose of the lot becomes driven by the rabbithole(s) that are on it and not so much by the community lot type. The usual choices for a school or career building lot would be Visitors Allowed (if you don't mind sims hanging around who are not there strictly to use the rabbithole, perhaps your school has a playground off to the side for example) and No Visitors Allowed (if you want sims to use the rabbithole and then leave after their business inside whether it be working, going to school, or something else has concluded). All of the other community lot types are really for open lots.
So, in the end, it doesn't really matter if you re-use the existing lot that a science center is on, replace it (if Edit Town lets you), or use a different lot entirely.
