[Mr.wreckless]

As per above, I definitely wouldn't drive very far with a downpipe without a proper tune for it.

That being said, the procedure isn't overly complicated, but Audi's can be a bit difficult to work on. If your car is old you can bet yourself the top 3 and bottom 3 bolts will be very stubborn and seized, not to mention the sensors too.

Anyways, if you are lucky enough to have the short version DPF/downpipe, then it is at least doable in a reasonable time, pending the bolts being cooperative.

There are 3 bolts by the turbo, easily accessible, though I would suggest getting a starter-motor wrench set which is curved, it'll make it a little easier to crack them loose, and possibly also new studs in case they get stuck and come out with the nut.

You'll need to jack up and slide underneath the car in order to access the bottom 3. From memory 1 of them is a bolt with an internal male nut pattern just below the bolt top which in turn locks into similar female bolt pattern on the DPF for lack of a better description. My guess is the Audi engineers made it this way because access is so restricted this way you only have to undo the nut on the underside. The other two I believe are standard bolts and nuts where you have to hold the bolt from one side whilst cracking loose the nut on the opposite side.

Pro tip to get the DPF out is to remove the false firewall/torpedowall. You'll probably have to undo a brake booster vacuum hose that runs through it but you won't be able to lift out the DPF with the wall in place. It's the piece covered in heat wrap behind the DPF, easily visible in the engine bay but perhaps not so easily visible to see it is removable. I have seen threads on the forum of someone linking to the appropriate Elsawin technician page for instructions too, so it is available if you google.

After the DPF is out you can remove the sensors and transfer them to your downpipe.

I'd advice getting plenty of WD40, a torch to heat things up if you need it, a bag full of applicable and suitable swear words and some patience. I wouldn't do this job somewhere the car couldn't be parked up for a while in case you get stuck or break a bolt or so. Extenders and some universal joints will make it possible to access the difficult nuts and bolts, you won't get a regular wrench on them due to the tight space.

Good luck!