Yeah, what I said earlier was just an idea for those that were looking to use this sort of thing. IMHO and RAW, a caster should be able to prep or willingly cancel prep at there leisure. My thoughts were that if you wanted to make spell casting more deadly, if prep is violently interrupted in some harsh and extreme manor, a penalty could ensue. Of course losing the prep is penalty enough for me.
For my games, spell prep is preparing to cast a spell, not a specific spell (which may not be RAW). My reasoning is that RM uses PP and not material components, like other game systems. If RMC uses the greatest penalty/bonus on the prep table for all of the 1-9 rnds of prep, then it maybe it is a specific spell. I play RMFRP and I know the OP stated that this was a RMC question, but it is interesting, RAW or not.