I also work for a dealer not VW mind but its in the VAG Group.
When certain work is undertaken on your car then the technician needs to drive it A) to diagnose the problem B) to ensure he has rectified the problem. Its all to ensure that the repairs made are good enough to be released to the customer.
If you are a trained technician and understand fully how your car woks then yes leave a note saying car is not to be driven if you are not trained in such matters dont as if there was still a fault in your car you would be the first person standing back at the reception desk shouting and screaming as your car aint fixed trust me it happens
I also take great care in my car but there is alot more to worry about in life than the thought of someone else driving my car hey they cannot drive it half as bad as i do anyway
And on the remap front i have mine done i have no intention of informing my dealer it has been done but if they ask i will tell them no point in hiding it.
Bit of a rant here but hey! peeps be nice to your dealers even if they are twonks the nice freindly customer will have a lot more done for them than the awkward arrogant sod who threatens court action every time he gets a bill for oil disposal. Its alot easier to just do the work than spend days arguing with a customer about the remap on his car invalidating his warranty. If you dont llike you local dealer find another one. Simples