I think Castro and Romero stay about the same. There would have to be an influx of new prospects to bump them down. I think their rankings are kind of sticky.
I'd be surprised if Bleis or Cespedes dropped below 30 during the season. Bleis will be at AA and they'll give him the benefit of the doubt as being young for the level. Cespedes will probably start in High A and should have better offensive numbers than last year (Salem is a horrible park). There's a case that they shouldn't be top 20 guys, but I don't think they fall into the 30's.
Guys I think could fall: Uberstine, Mullins (high BB rate), Johanfran (if his bat doesn't bounce back), Taylor.