music organization in my library

I was manually deleting some duplicate songs in my R&B genre and accidentally deleted the whole group. I pulled the songs out of trash, but the genre title is gone and I can't figure out how to add it back to the genre list so I can choose songs from that group. They are all songs ripped from my CD collection and there are a lot so I don't want to reload them from the disk. Along the same line, some of the genres Apple assigns to my music make no sense, is there an easy way to reclassify music so the assigned genre makes more sense?