Automatically uploading themes to S3

[CRGabo]

Hello! I am currently looking for a way to automatically upload images to S3 whenever I modify a theme. This images are saved under /themes/THEME_NAME/img. I can upload products without a problem since I can attach my code to the addProduct hook. In this instance however, I haven't found a hook that does the trick. If I were to make my own hook how can I contextualize it so it is only triggered whenever the "upload file" button is pressed?

I think I need to modify the source file that handles the upload. I think i need to add my code directly there, however I would prefer not to do that. I would rather solve this problem with just a moule. Is it possible?

Thanks in advance!