pscan.uk

If you want a spare SCU then you will need spare key fobs to go with it.
The fobs have a "rolling code" and so even if you cloned them from one SCU to another, eventually the code would roll out of the window of the one that's not in use and they would no longer work.
The T4 can reconfigure an SCU from one car to another, but, the fobs always stay linked to the SCU that they are linked to.
I can probably pretty much clone the T4 feature, but it will have the same limitations.

So, if you buy a second SCU make sure that is comes with its own key fobs.