It is possible to do this. It is a labour intensive process. You do need to be careful to avoid scratching the glass.
Cut through a lead line and carefully rip away the lead tape, being careful to not pull so hard that you flex the centre of the glass and cause it to break. You will need considerable force. The bulk of the lead is probably positioned over the film, so bulk of the the glue residue from the lead tape will come off when the film is peeled away. With a spray bottle mist the glass with white spirit and scrub using a cloth. If the glue is especially resistant use a broad wallpaper scraper and cover it with the kerosene soaked cloth to scrape the glue off. Use vinyl or latex gloves.
However, the manufacturer comments that stained glass overlay is virtually impossible to remove. It is better to replace the glass. It will save time, expense and possible tears.