Congratulations. This watch was my 2nd IWC!
Congratulations. I believe the GST Perpetual to be one of the best values in perpetual calendars - such amazing complexity in a sporty, durable package.
I also have the saumon, or salmon dial version too. There was something so unique and eclectic about the contrast of the saumon with the blued steel hands against the polished steel case/bezel.
This was my first perpetual calendar IWC - I bought it back in 2002 - and I just love everything about it - in fact, I am wearing it today for the first time in a long while - coincidentally.
** With regard to your question about additional dials and swapping hands, etc - this would be rather pricey - and require sending the watch out for several weeks for service.
Now, I am just estimating some costs. I recently had my GST in for a typical perpetual calendar service - the dial was not replaced, but some simple lubrication and a case polish was about $1,100.
A "new old stock" GST dial from the factory would cost you about $250, plus you'd want new hands, another $100 - and the service to swap it (not including the parts) would be about $500 give or take $100. You would only want IWC doing this, in my opinion.
I have considered buying the Titanium version with black dial and yellow markers as a second GST....

My GST on the counter last spring