Thanks for the notation. It's my understanding (and I could be wrong) that the organizers in CA are predominantly ISI people and are not familiar with USFS rules. As questions come up, they are fixing things, hence the revisions. But I would think that if there haven't been any changes for a month or so, then it should be safe to enter.
I do know that if I found that a later change to the announcement forced me to change an event I'd altready entered, I'd balk - loudly - and being charged $10. If the mistake is on my part, though, (say I clicked on Pre-Juv instead of Preliminary), then I can understand the fee. A couple of the club competitions around here due that - but only after the deadline. It teaches people to read announcements and fill out forms carefully.