[TYPO3-formidable] Modify js_calendar theme (secure against extension updates)

[Martin Terber]

Hi, I am using the Formidable renderlet:DATE (with js_calendar)
How can I configure Formidable so it uses a theme that I store in my fileadmin folder? I need to avoid that modified files will be overwritten on next extension update.

I need to replace:
- ext/ameos_formidable/api/base/rdt_date/res/lib/js_calendar/img.gif
- ext/ameos_formidable/api/base/rdt_date/res/lib/js_calendar/calendar-win2k-1.css

Thanks for any hint.

-- 
Greets:
Martin Terber
www.martinterber.com