Perhaps there could be an option of choosing between standard castling and free-castling?
What do you mean?
Free-castling was the style of castling employed by the Italians up until the latter part of the 19th century. The Russians also used free-castling but abandonned it slightly sooner. It's a looser version of castling. Consider the squares from the King to the Rook (including their own squares) as the unit. The Rook moves to any square in that unit, other than his own square, and the King can move to any square on the other side of the Rook.
Never heard of free castling so I looked it up. Don't know about the Russians, but it was indeed a regional variation used around Italy until the late 1800's.
Weird.
when the wimps took over chess they brought in the castling rule, to top it off they then didnt even allow the kings to tackle each other, a far cry from a king being chased into a corner by another like two kung fu fighters.