I have just upgrade from ERPNext: v10.1.27 to v11.1.11.
But when I change UOM in both Sales Order and Purchase Order, only “UOM Conversion Factor” and “Qty as per Stock UOM” will change, other fields such as “Price List Rate”, “Rate” and “Amount” remain unchanged.
The PR is for v11, however, it should easily work with v12 too. If it works out for you, leave a comment on the PR so that it gets more light and gets merged into the main repository.