It's been many years since I re-addressed TIUs, and my memory isn't as good as it was in the last century, but I seem to recall that if you take a new TIU, which comes with its address as #1, and readdress it as #4, all locos in the remote which had bene on #1 now move to #4. The trick was to save the remote's data to a computer, re-address the new TIU, then restore the data from the computer. The add the new TIU #4 to the remote.
I can't imagine wanting a layout in which only one TIU was used at a time. While all remotes can have the same ID, my recollection is that TIUs should not. Having gotten everythong set so it works, years ago, I no longer remember how I got there.
