What SHOULD you be allowed to do in a control zone?

Once you start naming specifc things you can do, you're opening a serious can of worms. Because things not specifically mentioned as either prohibited or allowed, becomes a source of interpretation at some point... it just will... period... it's most likely a rule of nature, or somewhere in Murphy's law, if not both.
So either make an exhaustive positive list of allowed things, or an exhaustive list of prohibited things (and I would sincerely suggest the first).
But if you do so, expect nagging about why this or that isn't included, arguing that this or that activity is similar to one that is allowed, only slightly different, etc.... Aka organizer/judging nightmare.
Also the more activities you allow, the harder it is to enforce. People (marshalls, competitors, etc.) need to memorize a bunch of stuff, and keeping an eye on whether what the competitor does is allowed or not, becomes real hard...

Now, since I'm in a different part of the world, I could care less about your rules since they will never affect me. But i think it would be a damn shame to make something that people could squabble over, thus I suggest that you make a "once checked in, you can't do anything. If you need to do anything between stages, check in late and take the penalty". At least that's how it works here in Denmark, and I think it makes sense for all the above reasons.

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Brgrds
Brian