I once read something on schneiders website that warned of moving lenses from shutters other than the original. They said each lens specifically shimmed for the exact shutter and that there were slight differences from shutter to shutter. I have seen lenses of the same model and focal length side by side with shims of slightly different thickness.
I've also heard many people who say that swap their shutters and don't notice the difference.
It's possible that that LF lenses would be more forgiving as they are used at smaller apertures.
The fact that one could call the fitting process for helical mounted lens to a technical camera shimming has nothing to do with using shims to optimize the spacing of lens elements to a shutter.
If there is a difference from shutter to shutter, two shutters might randomly match. So consequences of crude shutter swapping might be non existent in some cases.
In the end your mileage might very, and if it works for you than do it.
I do think that if one ever has to sell a lens that he or she knows is not in its original shutter, than he or she is morally bound to share this information with the new buyer in case of the possibility of quality degradation. One should should add who and how the swap was preformed. I personally would want to know if:
(A) you know that the lens was reoptimized on an optical bench for the new shutter
(B) if the new shutter was precisely matched to the old one by measuring the original shutter and with micrometer accuracy and reproducing the distances on the new shutter (via reshimming if necessary)
(C) The lens elements were simply unscrewed from one mount or shutter and crudely transferred to another without regarding to minute differences between the too.
Perhaps lenses mounted with method C are still good. If one has actually used and tested a lens after it has been transferred then that could and should be mentioned.
All copal 0 shutters are the same 'thickness' for this purpose. The shimming is performed by a circular metal shim (similar to a washer, in some insane thickness - e.g. 0.001mm) if needed. So, if for some reason at the QC stage the lens needs shimming, i.e. the front and rear groups need moving further apart, then a shim will be inserted (usually behind the front group).
In all my time I have only seen one shimmed lens 'from the factory' - a Schneider 72mm if I remember correctly. I've replaced shutters on lenses many, many times - with absolutely no observable adverse affect.
N.B. This sort of shimming is usually done by Schneider or Rodenstock in-house. The sort of shimming that Alpa and Cambo do when you send a lens to them to be mounted relates to getting the lens to focus at infinity once installed on the helical and mount. This is usually done by removing a few screws on the helical, focussing the lens at infinity (on a test bench, shooting tethered or whatever), setting the ∞ point and retightening the screws. Thomas has a good summary here.
