Would it be possible for a borrower to have the ability to temporarily borrow the knacks of others around them? (I’m thinking something like their own knack being the ability to use the knack of the last borrower they touched.)

I’m sure it’s possible, but it would be a knack that takes a toll on its user more than a regular one would. Borrowers aren’t quite X-men level with their abilities. They come with severe disadvantages and start out weaker to begin with.