Not sure if there's a way to change positions beyond just editing the player, but when trying to set up my 34 defense I noticed all my DE were ~250lbs; this would not be sufficient to play the 3 technique so I tried to change some of my talented reserve DT to DE...their overall ratings suffered as a result, and I assume would provide me with poorer results through the game engine.

Is there any way for me to feel like I'm recruiting, coaching, developing guys appropriate for my system here or should I just pretend they are big boys and leave them at DE? Was hoping I could move the DT to 3-4 DEs and then turn the lighter DEs into 3-4 OLBs.

You have multiple options:

1) Edit the players and raise the weights... probably not a good idea long term
2) Keep the players as DT, but then play them in the DE slots of the depth chart... no position change required.
3) Ignore the OVR rating and play the players you want even with position changes... the OVR will recover a bit as the player skill goes back up

However, the engine tends to focus more on relative weights than an specific number. And it focuses more on underweight versus overweight... so bumping a guy at 250 to 260 for realism isn't going to have drastic effects on results. Putting a 200 pound corner against a 300 pound lineman would affect things a lot more. Either way the game still puts a higher priority on strength, tackling, etc. and then on skills, and then weight effects get factored in. So I wouldn't put a 50 strength guy in my depth chart over an 80 strength guy just because one was 300 pound versus 280 for example.

This is great insight, do we have a table of ideal height / weight ratios for reference? That would be a key element to know to understand if a player is underweight / overweight by the game's parameters.

Thanks.