I have removed the gasket many times. I use your method, Raf. Ie with a flat screwdriver. I don't think it is a good idea to remove the shower screen and pull the gasket out that way with the VBM, because I have the impression the shower screen is quite vulnerable. Having said that, if all E61 groupheads are the same, then Carolyn is more of an expert than me, and go ahead!
Anyway, you need to be a little bit rough to remove the gasket and it may damage the gasket a little bit. If your gasket is at least 2 years old or you have always left your machine on, you may actually irreversibly damage it (and you will know!). I recommend having a spare one first!
I am not too sure it is a good idea to soak the gasket in Urnex. Urnex is really aggressive stuff, but you can give it a try of course. You may want to soak the shower screen though... you will soon discover how dirty the screen is and the grouphead behind the screen.