How to do some changes at server side using SOAP UI

I am using SOAP UI to create a mock service.I have a folder which contains all my xmls.The SOAP UI works in such a way that what ever xml is put in the specified folder, will be available on the network. Then i can perform a GET service to get the contents of the xml. Now i need to perform do some value changes in the xml.

Can i perform a POST request and changes the values of the xml? If NO, then how can i achieve my goal?