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.
=CONCATENATE("SS",TEXT(NOW(),"yymmddhhmmss"))


If you want to get started with RSAT.
Download the tool and the user guide from here.
https://www.microsoft.com/en-us/download/details.aspx?id=57357

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