That only works in theory if you actually change how YOU play the game. You can change your scheme/player type to get an boost to the Overall rating for your LOLB, but if you still run a 4-3 defense he's still going to play like his rating BEFORE you made the change. i.e. if he's a 70 4-3 LOLB and a 85 3-4 pass rusher but you play him in a 4-3 he's going to play like a 70 NOT 84 regardless of what scheme/player type changes you made.
The bottom line is that Overall rating is purely aesthetic. It has about as much direct impact on the game as the jersey number.