Well, I don't think the game should prohibit moves per se regardless of any range or whatever. Numerous positions have good crossover even if it doesn't seem obvious. Some of the better projects I've had have been non too obvious changes.
Look at Miami irl - Tannehill at College primarily WR, something like 14 games as QB? Tony Lippett, overwhelmingly WR now being used as CB ( admittedly mostly because he's 6ft 3, meaning he towers over the other dwarves we have on the roster ).
What's needed really is a system where owners can take chances on moves like this - maybe with a higher risk of them busting?
If it's a case of owners gaming the system by changing position, then one workaround could be to simply base contract negotiations on their main, "best" position.
Example;
D. Odgy owner wants his 4th year star QB reclassified as a C to lower contract demands. Ok, His assigned position may now be C - he's had 1 day at that position. 4 seasons as QB, so he'll want QB money. D. Odgy releases him, hoping nobody notices, he can resign him cheaply. Oh wait, that QB wants a large truck of money to be delivered pronto - he knows his worth because he's a QB and not a C in his own mind.
Say D. Odgy decides he wants to become a pillar of society. He swallows his pride, pays the man his QB money but wants him to remain as a C; maybe he might be better there, anyway. D. Odgy just drafted another QB. He'll have that C as a project, give a 5 year deal - sadly on QB money.
End of that contract, wouldn't you know it, that C is now a MFN version of Dwight Stephenson ( without the Jets cheap shot ending his career ). D. Odgy resigns himself to paying more QB money for a C - but wait. After that 5 year contract ends, he's more experience as a C so is now happy to accept C money...
TL;DR version
Have players have their own notion of their main position. That would be the position at which they've accrued the most game time. Contracts would thus go on that main position value, preventing the fiddling of positions. When another position has had more playing time, then that becomes their new main position.
Probably needs work and has a millions holes in it, but that could be a first stab at blocking the problem in hand.