I have a suppressor that unscrews into sections. Can I pin it to make essentially a 16” barrel rifle even though it comes apart for cleaning?

What is the specific model of silencer you have?

In its shortest fireable configuration while disassembled, will it still be over 16"? If not then it's an SBR.

You don't get to pin a mount or blast chamber to the muzzle and then claim the total assembled barrel+silencer length... you only get to claim the barrel+fixed blast chamber length. I suggest you plan to either use a monocore supressor or one in which the full length of the outer tube is affixed permanentky to the mount-nut or and/or the barrel instead. Pinning a modular suppressor (like a Q erector) makes very little sense.

Thought as much, thanks.

Doesn't seem like the OP wants to say

Must be a Rebel Silencer