Use the sim.can_move function

It looks like sim.can_move(tpt.el.prot.id, tpt.el.brck.id, 0)

for can_move, 0 means "don't allow pass through", 1 means "swap positions", and 2 is "pass through - occupy same space".

This function is present in the current version of the game, but is very unreliable and prone to being reset. The next version of the game fixes this so that can_move changes stick. Plan is to release that version this month (although I made that plan before having several huge distractions this month).