You could always gets some steel plates cut for all the back sides of
changer and weld them to case, with a another
lock over the
lock. I don't think in the stock form one
changer is any tougher than the next. An alarm and inside and outside cameras would do more for you along with possible lighting changes.
I myself leave the keys on a magnet tag on the side of the
changer so less damage would be done. Once again high security $1tokens seem to kill the thieves energy for breaking in also . You can't make everything bulletproof, but a combination of things will make you look unattractive to all but the hardcore idiots, at that point its best to just try to minimize damage so that you have very little downtime, and large expenses.