Unfortunately, the Q&A seems to be explicit on this point, as are the rules. You’re limited to exactly what’s on the form, listed by model. (Functionally-equivalent, but physically-dissimilar choices are not permitted.)
This is a real source of consternation for inspectors. The DP and the DXP are functionally identical when only the clevis attachment is used (as if it were a DP). It’s very annoying to be in a situation where the absence or presence of an unused external screw thread makes or breaks a team’s inspection. And it happens all of the time.
The trouble is, it’s really easy to miss this. There are plenty of times when a cylinder is mounted so that it’s inconvenient to read the stamped model number on the side, so physical characteristics are used to identify it. It’s not hard to overlook the screw thread that teams are not using, and move on to the important issues during the inspection.
Add to this the fact that many of the inspectors don’t know what to look for, because they haven’t familiarized themselves intimately with the Bimba catalogue, and you’ve got a recipe for inconsistency. Realistically, with most of the inspectors only volunteering at one event per year, and with many having limited FIRST experience, it really is too much to ask to have them verify every cylinder in the manner that FIRST describes. (And they can only report it to the lead inspector for verification if they recognize that there’s an issue.)
This is part of the reason why the pneumatics take up a vastly disproportionate amount of inspection time, relative to their utility. It would be far simpler, if FIRST simply attached and referred to pages from a particular Bimba catalogue, and stated that certain model ranges were permissible. Bimba would still be free to offer whatever particular models they desired, and would retain the (nearly) exclusive branding of FIRST cylinders. But the teams would be free to get a wider variety of parts, and the inspectors would only need to verify the series, rather than the particular special features of the cylinder.
For example, if you’re not using the magnetic piston (M option), it’s functionally identical to the standard ones. The prelubricated cylinders (G option) are identical to regular cylinders lubricated after purchase with a kit from Bimba. The DP is the same as the DXP, when the threads are unused.
FIRST could even take this a step further, and open it up to all manufacturers, if the arcane pneumatic sponsorship framework could be revised. That would be the easiest thing for the teams. (In this hypothetical case, teams would need to be able to prove that their cylinders meet the same specifications as the Bimbas, but a catalogue would easily satisfy this.)