Don't tell then and you can't claim when it goes missing retrofit or not.
I told Audi insurance about my retrofit extras with no increase in premium, they are listed on my paperwork and therefore covered by the policy.
Depends on insurer as with some you now have to declare factory options upon insuring the vehicle so if you change the spec and dont tell them they could get ar53y if they noticed.
I told mine about the options and the premium reduced It was only £4 but it still went down - could be an error, but is what I didnt want in the event of a total loss is not getting the cost of these back again.
Trust me i have worked in the Insurance industry for over 15 years..
No Insurer would check if your RNS-E was retrofit or factory fitted if you needed to claim for it, by telling them you are giving them the option to refuse to cover it as it is retro fitted or ask you for more money on your premium.......
IMHO you should tell the insurance company that you have a Audi sat-nav unit. I very much doubt they will be able to tell whether it was factory fitted or not. Most Audi dealerships can't even decipher the options codes for our cars, never mind the insurance company.