I love it. I definitely would like for Barnabas to meet all of Knife's other selves. It's funny, cuz Barnabas is in league with someone in canon who also takes on different identities as per the situation, and their default self is white hair/skin, very changeling-like in that regard.

But yes, go for it! The theft would be happening at the camp, I imagine? Cuz the alternative is Stonhyrr (his fortress), and that isn't impossible, but the camp is far simpler an endeavor. I'm fine either way, whether they thought about the Barnaguise before camp or during, just very different experiences for Knife to acquire some clothes!