How to manipulate excel data?

Hi

Can someone please assist with the following test steps, I need help with the test step in bold as below:-

I am using SoapUI Pro & issuing REST requests.

• Generate an excel file 
• Issue a Post Request - I Upload the excel file via an attachment  (I will call this File 'A'/Master Copy)
• Using File 'A' I need to make any small & non-specific change (for example, there is an excel column called customer name) for the sole purpose that I create a new file called File 'B' that is very similar to File 'A' but not identical 
• After creating File 'B'  I will upload this file once again via a Post request using an attachment 

Can anyone advise me how to do this?

*If scripting is involved can you please include clear comments for the purpose of my own learning.

Many thanks in advance