I checked with the team on this, there is no way to change the variable of a specific submission within an instance. The variables changed from the monitor page are appended to the submission history. This is mainly because we have to support auditability of the values present at submission time. If you use a custom report you will look at the latest variable values which in your case would contain the admin changed values.

Just to make sure I understand correctly, the built-in Forms reports only go off of the original submission and if an Admin changes a variable, it will not be reflected in the reports. If I use a custom report, then it will reflect those latest variable values. Does that sound correct?

If yes, is there any way that the built in reports could be updated to show the latest variable values instead of the values from the original submissions? Maybe under the "Form" drop-down have an option that says "Current Process Data", similar to when selecting which data to use in a Save to Repository task in Self-Hosted?