To some degree, I get not allowing us to edit roles; you'd be fundamentally changing how a player plays the game. A coach can maybe nudge a guy, or coach him up and improve on areas where he's weak, but I can understand how it'd be "unrealistic" for a coach to change a player who is a sniper into a pass-first playmaker. It's a mentality, not a skill.
THAT BEING SAID... there's not many grinders in the draft (in my experience, at least; particularly not at the top end of the draft). And that makes sense; few NHL grinders were grinders in juniors or college; they were all scorers who weren't good enough to continue to be elite scorers at the next level, so they had to adjust their game. Not being able to "downgrade" a player from PLY to TWF, or PWF to GRN, is definitively unrealistic.
And, I've said on here several times and will continue to preach it: it's a video game. If we want to "abuse" a customization option to "cheat", who cares? EA shouldn't be policing how we play the game. Their job is to make it as realistic as possible, then allow us as much customization as possible within that framework.
We should be allowed to make CPU-CPU trades, force retirements, edit draft classes, edit player stats (my character in Franchise mode was created to reflect my Be A Pro from NHL 12, but my CHL stats were significantly better than the underwhelming stats he simulated prior to entering the draft in my Franchise mode; I really don't see why I'm not allowed to fix that).
Greater customization would allow us to make the game *more* realistic, by having guys retire at the right time (rather than a Hall of Famer hanging on for 2-3 years in the AHL), or forcing trades that happen in real life that the game thinks is unrealistic (and that don't involved our team)... and if it makes us happy to "abuse" that customization, well... it's a video game. That's the whole entire point.
And, of course, if "realism" is all that matters, then not being able to edit position is still mind-bogglingly stupid. All left-handed defenders should be listed as LD, with RD as a secondary position; I should be able to fix that when I see a CPU-generated prospect that is wrong. If a player I draft and develops spends 12 years at RW, he shouldn't be listed as LW just because he played LW one season in juniors over a decade ago. Goalies shouldn't have secondary positions, and I should be able to fix that when I see it.