[DonRotolo]

You could, but be sure to word it carefully.

As I see it, what you want to do is this (correct me where I am wrong):

Start the match with only the clippard tanks at pressure (allowed per <R01a>. Or don't, and let them pressurize during autonomous)
After start, open a valve to extend a piston.
Mechanically limit the extension of that piston to something like 1/2 its stroke.
Allow the back end of the piston to completely pressurize to 60 PSI or so.

So far, are we OK? If not, I'd need to see a rule.

Using some mechanism, release the mechanical limit, allowing the piston to extend the rest of its stroke.

Still OK, right? Assuming you follow the rest of the rules (e.g, perimeter and safety), it still looks OK to me. (My opinion is worthless at any competition though)