Good info JetTurbo. Most circuits have a range of impedences that it will tolerate,...
That is true, they are more tolerant of high current draw than low current draw though.
I run a 50W halogen bulb in my lone backup light, a little more than double the normal 1156 bulb's 22W.
Been running it for about 100,000 miles with no issues.
(Tried LED in the backup light first, but the LED bulbs made such poor use of the fixtures reflector,
the result was dimmer than stock. :thumbdown
... so you may be able to get away without the canbus fix. ...
On the mk5 turn signals, it will be up to a lone bulb to do the job.
There is no VAG-COM mod that can disable the active monitoring of any enabled exterior light circuit.
I have read reports that the 1156 5W
Eagle Eye 5 Luxeon / SMD hybrid LED bulbs from autolumination
do draw enough to satisfy the controller, but I have no first hand experience with that bulb,
as it will not fit into the GTI's front turn signal fixture. (and at $20+ per bulb, it is not cheap).
For example, switching EITHER the city lights OR the sidemarker bulbs on a Rabbit to LEDs will not trip the error signal and turn off the entire circuit, but switching both will cause it to shut off....
There are four circuits on US mk5 VWs that work that way (three exterior, one interior),
where two low wattage bulbs share one CEC circuit.
(1) Front left city light / left side marker light, (2) front right city light / right side marker light,
(3) two license plate lights and (4) two footwell lights (if equipped).
In those four cases, each circuit feeds two 5W bulbs, and the circuit is
programmed to continue to operate if only one stock incandescent bulb remains functioning.
i.e. with stock bulbs, only one is needed to keep these circuits alive.
In stock form,
both incandescent bulbs must fail before a lamp out is triggered.
So if you change only one of the two to LED, the remaining incandescent bulb
continues to provide enough current draw to keep the controller happy, as you describe.
All other exterior lamps have higher draw bulbs (more than 10W) and
dedicated circuits for each individual bulb.
i.e. there is no second bulb on any individual turn signal circuit to keep the controller happy,
left front, left rear, right front and right rear are all separate discrete circuits.
BTW the mk5 does not have a traditional turn signal flasher, the CEC digitally provides the flashing function.
i.e. Electronic LED Flasher replacement is not an option on our cars.
... And wiring in a small resistor is definitely not a difficult task, but it does make it "not plug-and-play," like you said....
Difficult - no. Certainly it is possible to modify the wiring with a load resistor safely,
but anytime you cut / splice exterior wiring, you run the risk of moisture getting into the new connection,
which over time will corrode and cause the circuit to malfunction.
Care must be taken to seal it up good to avoid future issues.
Although it is possible to tap into the turn signal circuits in the interior at or near the CEC,
that adds a little more complexity to the task (interior trim removal)
and makes safely placing the heat generating resistor a little more of a challenge.