Indeed I had thought really for this... because I have, over that my "contemporary" sax, also other vintage horns and therefore happens that they don't play for long time but I would like to hold the pads in good form to avoid deformations Is the use of the clamps practicable for this? They don't ruin the satin silver finish making marks?

no they dont ruin the finish. If by chance they do leave a mark you can simply polish it off. Whether or not it is practical is up to you. do you wanna go through the trouble of taking care of those?

I like to take care of my instruments... but since I have made to install professional (and expensive) pads, I don't want that them not seal well after a period (not years!! a few months) of stop

I've never had much trouble with leaks, even when my horns have been in the case for months at a times, even without using key clamps. No, the higher tension should not cause the springs to break, but logic tells me that eventually, if held in higher tension for long periods of time, the springs would weaken, and you would not get as good response in the keys. This would likely be so slight as to be unnoticable, though. Using key clamps to seat the pad originally may be fine, but unless your tossing the case around with the horn inside, clamps should be unnecessary. Plus, I wonder if you might risk putting the horn OUT of adjustment if you install the clamps incorrectly. Swabbing three times after every use will take most of the moisture out of the horn, but some will remain. I wouldn't risk sealing that moisture inside with key clamps.