When making changes to a car setup, the aim is to just change one thing at a time, and keep everything else as consistent as possible, so you can really notice the difference your single change makes.
In the example of fitting a rear shock tower to the front of the TC3, my attitude is you should leave everything else (spring rate, oil, piston) as before. The only changes you may need to make to the shock is a slight change of pre-load to get the ride height to where it was.
The point of running the rear tower up front is the change it makes to the handling! You shouldn't make immediate changes to compensate for it. Just run it and work from their.