How do you modify data sets within guide-based GUI from command window?

I have a guide-based GUI that I am using to process data. Right now, the GUI takes in raw data, the user can change certain parameters of the processing and run the processing from the GUI's push buttons and edit boxes. I want to make it so that the user can modify the raw and/or calculated data between processes.

For example, if the raw data was entered, and then the user ran the calculation, I want him to be able to do say "handles.RawData = handles.RawData*5;" and then run the simulation again. Or, as a second example, he could say "handles.CalculatedData = handles.CalculatedData/2;", and display the modified data.

How would I go about doing this? I looked on here but only saw ways to display data from the GUI onto the command window, but didn't see much of how to edit the structure in the GUI-workspace from the command window. I also don't really understand how to use the Global function so if that is the solution I will likely need some additional explanation.