Had a play around and think I could get this working. Unluckily for me it would mean re-writing quite a bit of my program to get working. Also my current program loads in a pre-made .xml file and does a 'replace' of certain headings / values. It actually works really well as it keeps heading formatting (Colours / fonts etc..)
It just lacked the ability to save as a proper excel file / support pictures. Maybe I can 'merge' the two ideas together so I can load up a pre made .xlsx file and update the text in certain places / append a photo.
I've attached an example capx below which shows very simply how my app runs. (Two files in the project, the xml file which is used and works and an xlsx file which I have been unable to get working which contains a shape as a picture reference).
https://drive.google.com/open?id=0B33gt ... WRXZEhqeUE