In general there is no problem with config loss when doing an upgrade of code, especially if the upgrade is a version upgrade and not a change of feature set. As long as you assure that the new version of code is correctly loaded in flash and tha the boot variables are correctly updated then I can not think of a reason why you would need to reconfigure the switch.
If you are really concerned about this then I would suggest that you start with a single switch and try that one before you do a group of them.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...