One way you could speed up ticks would be to scan the AOE for TileEntities that implement ITickable and then manually call update(). Since update() is also being called by the game tick clock, any additional time you called it would speed up any machines in the area. Obviously, this is basically the definition of a lag machine, so make sure any loop code you add is as lean as possible.
I have no idea how you'd slow down tick clocks. You could easily do it for TileEntities that you control by simply skipping update() ticks based on a state. I don't know if there's a way to do it in a general-purpose fashion.
I know that there are items in mods that speed up ticks. If their code is public, you could certainly scan through their code and see how they do it. I don't know if there's any objects the slow down ticks. If you know of one, see if you can find code for it. If not, it may not be possible.