Yes. They may INCREASE the skill shard number. That's what happened when Tailgunner got a revamp. I don't think they would ever reduce the skill shards, that would be silly of them to do. but they may increase to allow more "power" to some moves.
Honestly though.. Rainmaker is such a skill shard draining character taking I think the most, if not close to the most, of any Eddie. I can't see how giving him MORE skill shard slots would be beneficial overall. He's got decent moves, they are just a bit underpowered in today's playing field (and having little or no yellow/grey buff abilities). My biggest bitch about Rainmaker is that he's always been way way way way too low for base HP, MR, and DEF stats.