u/Separate-Still-1616

If I have a raid1 with device A and B. Can I just keep A without having to rebalance data, and at most only change meta data?
It does not seem possible because if I do "device remove" I get an error that you cannot remove a device from a 2-device raid. You first have to convert into single mode which result in data rebalancing which can take a lot of time. Then you can remove the device and half of the data needs to be moved again back onto the remaining device which was completetly uneccesary in the first place because at the beginning it was already all there.
It should actually be an operation that does not need more than to rewrite meta data. So is it possible somehow? And if not, why?