Hi,
basically you can create overrides of all files in the components/com_visforms/layouts folder in your template (
www.vi-solutions.de/en/documentations/vi...layout-with-override
) as well as of the files in the components/com_visforms/views/VIEWNAME/tmpl folder. (These are standard Joomla! features). The overrides in your template are not changed, when you update Visforms, so your code would be save there.
Nevertheless, as I'm continiously developing new features and try to improve Visforms, I sadly quite often have to change some of the files mentioned about. So although your overrides are not touched by an update, Visforms may no longer work, because your override file might miss something. So you might be required to adapt your override after a Visforms update. And the changes I make are sometimes quite severe.
I don't know which Visforms version you use, but just in Visforms 3.8.9 which was release only days ago, I added an option to the file upload field, which allows you to dynamically add a "remove selection" link to the upload field if a user has made a selection. So mayby this is just the feature you are looking for? Then maybe try Visforms 3.8.9. But as this is still a beta version, please make a full backup of your website first, so that you can return to the old state, if you are not happy with Visforms 3.8.9.
Visforms relies very much on and uses lots of Javascript (especially for the browser side form validation). I actually do not recommend to try to add custom javascript to Visforms (especially to the submit button) because this button strongly interacts with the validator plugin and your code will most probably not work as expected.
Regards,
Aicha