The existing thrusters are all well and nice for controlling the orientation of your ship, but sometimes you might want a more energetic push. I therefore suggest that engines can be mounted in any direction the player likes, and bound to a "manual thruster group" analog to a weapons group. They will then work as an unidirectional thruster. An engine that points rearwards automatically becomes part of the normal engines.
The flip side could be that there is no automation to this. If your re-purposed engines' thrust does not go through the center of mass of your ship, they will make it spin. If you kick your ship into a spin with your pseudo-thrusters, there will be no automatic counter-thrust to stop the spin. If you also have normal thrusters, those will eventually stop your ship spinning, but slower if you reduced their size in favor of your "manual thruster group".
In practice, I wanted something like that for braking. Then I found that right now, an engine can only point backwards. Annoyance occured.