The only way to do that for a project that contains enterprise resources is to override the max units per resource at the time you edit the project. Local resources will maintain max units, but enterprise resources will be reset the next time you close and reopen the project. This is an unfortunate consequence that needs to be done if you are managing resource utilization. In Project you can keep a note someplace, keep a table in a report that you can copy/paste, or copy from an Excel workbook. Best I can tell you.