Kia ora Abdal
What you describe is what I tried before. However, when I set the "end" date of the first series to today, if I have made changes to any of the previous occurrences in the series, I get this message:

In other words, simply ending the recurrence and starting a new series at a changed appointment time does NOT retain the previous history (which includes Cancels and No Shows). What can I do to avoid obliterating my clients' attendance history?
This is dead easy in the Google calendar, where you have the option of editing 1. this occurrence / 2. this occurrence and all subsequent ones (which doesn't change previous ones) / 3. the entire series. So if Google can do it, surely Microsoft can too. The flexibility of the Google calendar is why I have resisted using the Microsoft one until now, when I had to for work.
There used to be a "wishlist" that users could vote things on to for future updates. This would be way up there for me and, it seems, for a lot of other users - there are variations on the same question in the database going back to 2016 - that's 7 years ago!!
I get that this is the community forum, but how do we get this message across to the developers? The Google product is simply better and they need to up their game.
Ri