The RSAT doesn't have any roll back feature. So, it can be frustrating updating the excel file with
unique records.

Well not to worry - RSAT supports Excel formulas. The user guide suggests using RandBetween(a,b) Excel function.
However, that isn't really reliable and you are hoping you don't get the same random number.

I have been using date formula. The below concatenates the datetime to the string.

If you want to get started with RSAT.
Download the tool and the user guide from here.

You can also watch a short video that walks you through how to use it.