renumbering switch stacks

Boot up one switch set it as master (priority 15)
set all its other values
Boot up  second switch set it as backup (pri 14)
and other values

Create the stack between the two devices.
Now add other switches to the stack and give them numbers etc.

set start priorty
provision switch 1 ws-3850-u etc

switch 2 renumber switch 1

Once you swap switch numbers you can't swap them again
Make the swaps you can
write mem
reload (takes about 10mins on 3850)

Check again
sh switch

Move the remaining switches