See, the thing with Carrie is the rights are unavailable and have not been given to anyone (except for Emerson College, and Stage Door did their production illegally, but the creators got wind of the production and actually showed up and okayed it), but both Emerson and Stage Door are very regarded performing arts venues and their chances of getting the rights were okay.
But community and regional theatres are screwed-unless they have a REALLY good reputation. Many a theatre have been denied to do Carrie: The Musical. Some have gotten away with it, others haven't.
If the theatre wants to even bother writing (although there's a 95% chance they'll get denied) they should keep a first second and third idea down and not get too dead-set on the idea.
For more information about rights for Carrie, you can PM me on it, as I am pretty knowledgeable on the subject.
Recent Broadway and Off-Broadway:: Carrie, Merrily, Ionescopade
Next On The List :: Clybourne Park, Once, Streetcar, BOM