Custom uploader
Jamroom Developers
the 'file' form_field type is registered by the jrCore module
/modules/jrCore/include.php
jrCore_register_module_feature('jrCore', 'form_field', 'jrCore', 'file');If you created a module that was processed after jrCore was in the startup process you could also register that same form_field then your version would be used instead.
As to whether it would break all the modules or not, that would have to be discovered along the way. Can't say for sure what issues you would run into because I've never tried. As long as you returned all the things the modules are expecting to see so they can continue it should be possible.