I had the replacement badge for 3 years, too scared to pull the old one off. It got so bad I painted it with enamel paint. Looked horrid, so when we had that hot spell thought I would tackle it.
Masked off all round the old badge and taped on a couple of old credit cards at the bottom of the badge and carefully eased a wide scraper under the badge and prised it up. When it moved I got my fingernails under it and it pulled off fairly easily.
Thought I would do the front badge as the rear went so easily, dont use a wide scraper on the front badge, the grill must be more rounded and the wide blade digs into the paint. Doh!!! Got a table knife when the wife wasnt looking, and slid that under the bottom edge, using the old credit card to lever against and it came off easily again.
Thats on a Mk2, dont know if the Mk1 is different. The Mk2 was a complete plastic badge.
Best of luck with it.