Wonder if we will see teams swapping players from forward to D to mix up the split they can protect or if there are rules on numbers of games they have to play at a position
I'm pretty sure I've read something about certain statistics being "admissible" for arbitration - goal, assists, points, maybe +/- (don't get me started), games played, TOI. Other stats aren't admissible - namely, fancy stats. But, either way, when they're settling on a certain player's arbitrated salary, the position of forward/defenseman has to be a factor in their arbitrated contract value.
I imagine the NHL will say a player's position is basically like pornography - you'll know it when you see it.
That said, there are players who cross boundaries, and who can literally play both positions. Brent Burns and Dustin Byfuglien are two legitimately blurry cases that come to mind - both played defense last season (AFAIK), but both have played forward.
Are there any other cases like this? I don't follow all 30 teams in great detail, but I can at least confidently say that there was no one on the Bruins the last 3-4 years who fits that description. Torey Krug played forward in ONE game at the end of 2013-4 when they were going through the motions. That's one game as forward, 240 as defense. (And five seconds as goalie. I'm actually not kidding about that - it happened last season. He made a great save, and instead of "Tuuuuuuuk", the Garden chanted "Kruuuuuuug".)
My guess is, if pushed, the NHL say "If a skater has played x number of games in the past y seasons as a defenseman, he's D. Otherwise, he's F." And my guess is that the threshold will be absurdly low. Trying to count Buff or Burns as a forward is clearly angle-shooting, and the 28 other GMs would call it in an instant.
Both of the two cases I know are Fs-to-D. If you had the opposite case, of a guy who played D in 2014-5 and before but went to forward in 2015-6, one could make the argument that they should count as D, since they're more versatile, and the D is a more "valuable" position.