What is being a 42R like? Is it difficult to reclass?

Yes and no. Reclassing can be as easy as passing an audition, or attending AIT. What do you play?

42R is an Army "Civilian Acquired Skills Designated" MOS. Passing an audition on an instrument takes some serious skill and I would go so far as to say that it's even more difficult if you play a rhythm section instrument like piano, drums/percussion, guitar, or bass guitar. (Those instruments need to know their theory backwards and forwards to a level other instruments don't to achieve basic competency in jazz.) I have advanced degrees in music and only barely made the cut, which is largely because I come from a strictly classical background as a musician, which is a good baseline but not the style for which the Army predominately uses 42R's. All that is to say that while 42R may not be the most "hooah" MOS, it's a pretty hard one to get.

You don't give info about yourself but you should already be proficient at an instrument or/and vocals. Audition information should be online. You might even want to contact a recruiter for up to date audition info. Is there a band at your current post? If so, try meeting them to discuss.