Build in pause

From OpenTTD

Build in pause allows you to build while the game is paused. This is very handy when you're rebuilding a huge station or a mainline in your network while not wanting to disrupt any trains running on it. This can also help to prevent crashes. This cheat will only work in a non-network game, as of course, there is no cheating in network games. Build in pause also allows you to use the dynamite tool while in pause.

It is considered a cheat.