[Pared]

You probably can't do it because of the way their rating system and trade AI works.

Instead of seeing Vinatieri traded for Ricky Williams, they probably decided to disallow trades with K/P. They probably also encountered teams trading for multiple K's and franchise freezing up because of a team's lack of P's or K's due to multiples in a single position.

It's a much simpler fix than actually fixing the trade AI to only trade a K/P for their respective position. More developers do things like this than you probably realize.