Hello Matias,

Unfortunately, this functionality is not natively supported yet, however it is possible to capture and create modified copies of the uploaded files:

That said, modifying the files on the servers side, if possible, is a much cleaner solution, as Javascript doesn’t support directly modifying uploaded files.
You can also use our SetHeaders() Method to send any additional data together with the files.

If you have any other questions, please do not hesitate to contact us again!
Best Regards,
Ivan Peevski
Smart UI Team