OK; that would require Bell to consent to the trade. I don’t see why he’d do that, to help out the Steelers. Based on how the situation played out between the two sides, I don’t see why he’d want to help them get more compensation for his services.
Also, the language you posted from the CBA said that the awarding of comp picks can change if the two parties agree. The link that
@Anarchy99posted seems to suggest that there was a change to that agreement in 2016.
If true, we are back to what I posted previously: Pitt would be risking the loss of any draft pick compensation (and relying on Bell being willing to consent to a trade where he gains nothing), by applying the transition tag. It’s not impossible, but I think it’s unlikely.