Thank you all for trying to answer, the guidelines are not clear and exhaustive on the certain details such as the ones I was seeking for. but no worries, I got my answer today with the direct experience.
So today my apple one expired. (I still had/have other non-apple subscriptions active but had canceled them so no future renews, so this means that to change region it fundamental that only the apple subscription actually expire. for third party its enough to cancel future renews). When I figured that my apple one subscription was indeed expired I simply proceeded to change the region to Italy, initially it wasn't working then I realised it was due to the fact that I had a family member active on my account, so I disabled the member and proceeded successfully to the region change and activate the new apple one subscription in the new country, before and after everything was still there, all my iCloud & files, all my music with playlists and TV movies I bought time ago. Another insight, at least until now all my apps available only in the US store (previous) are still updating no problem.
My guess is apple now offers a grace period for all our data stored in their services. So for people seeking for the same/similar advice, here is my experience, hope it can help others.
