Labtec, you may be reading too much into the phrase 'mechanical break-in'.
To the best of my knowledge, it's really just a settling in process that occurs.
I suppose it's kinda' like a new automobile where the engine needs to be pampered for the first 500 miles or so during an initial break-in period. Once that occurs, the engine then runs more efficiently.
The settling in for the racks occurs when the Audio Points and perhaps the misc. connections of the racking system or platform are mass loaded with the components or speakers and over a short period of time.
I did not believe it either when I first heard about it. In fact, I thought it a bit funny and paid it no attention to it whatsoever. That is until I experienced it. It's there, and it's rather drastic.
As for a break-in period every time a coupling rack is relocated? Since you must first empty the rack, move it, then fill the rack, it would seem quite similar to a first install. This is assuming that one is using mechanical diodes such as Audio Points under each component, therefore, nothing is going to be in the exact same place twice and hence the settling process occurs all over again. The only reason I can think why the settling process for a relocated rack is a quicker process than an initial installation is perhaps the sharp ends of the Audio Points are already conformed to the material they rest on.
Perhaps another can provide a more detailed or scientific explanation on this mechanical break-in process.
-IMO