The problem is, printers.xml is marked "readonly" in Windows. At least that was my default on Windows 11.
Solution:
Locate the printers.xml file in your Documents\meshmixer\printers folder, right click the file, click preferences and untick the readonly box. Then apply and close. Now all printer changes will be updated permanently as it's supposed to be.
That's not necessarily a Meshmixer bug, more likely an issue with Windows permissions supplied during the install process. A lot of this has changed since Meshmaker was last maintained.
