Resistor mod - Had one of these on the wife's Bora 115 for a while, improved power a little, though mostly at the bottom end, not so noticeable after 3k rpm, and when the bad weather came around made the car hard to drive with constant wheelspin so took it off. She's not complained so I'll leave it off.
You get what you pay for - a 75p resistor will as you say chuck fuel in by fooling the ecu, but to what long term detriment? Wife's was on for 20k miles, no ill effects, but it's getting near 100k now, clutch is getting worn, no use in speeding up the process.
My remap on the Leon sits in one of the spare ecu slots, easily changeable with Vag-com from stock and back. As far as I know there are 2 or 3 such slots to put maps in, I presume the revo just swaps between one and the other rather than flashing the chip every time? Unless the dealer looks in the other slots I can't imagine how they would tell it is chipped if you turn it off.
In my opinion, at this time of year you are better off NOT remapping. No traction in 1st 3 gears till 50mph, colder air=more torque=clutch slip. I never had any probs in the summer, but come the cold air came clutch slip big time, coupled with the zero traction in lower gears means it's not worth using for me right now.
When remapped the car seems to have better range though.
Am hoping to put a generic map on in the next few weeks, give less torque, less power, more drivability.