Hey, welcome.
Right now, it's not possible in the stock install. But it's a good idea. IIRC, someone had implemented that a while ago (if you do a search), in their template, to only show certain aircraft to certain ranks.
It's relatively "easy" to do, and I can post the code on how to do it, if people want. It's really just a few lines added to the PIREP form. But, that restriction will only be on manual PIREPs. Doing ACARS PIREPs is a bit tricky, because I can't restrict what they fly, or what gets sent to/from ACARS in terms of PIREPs, that's why I never implemented it (for instance, XAcars doesn't even send an aircraft type). But it's very simple to add it in the manual PIREP form, if that's what you're looking for.