In Audi/VW land they aren't piggy backs. 
They literally write in new software to the ECU. Often including multiple programs, including stock.   
IE: On my cars I have 3-4 programs to pick from that can be chosen using the cruise control stalk. IE: Stock, 93, 100+ octane etc.   
For service, you just select the stock program, let it write, then lock the programming. Mind you, I'm sure they could have a rep come in and find it with a fine tooth comb, but it's never been an issue to date...