Can a 2000 Audi a6 4.2 be made into a Audi rs6?

Answer 1

I don't think its a good idea to turn a 4.2 A6 into an RS6. But they are technically the same engine but the RS6 has twin-turbo.

in addition most of the parts on the RS6 are different to the A6 model. Audi generally revise most of the parts on the R/S/RS variants of cars and provide improved performance items.

For example on the original 8L shape Audi S3 there were very few parts that were interchangeable between the normal A3 and the S3. If you want an RS6 it will be far cheaper to buy one than to try and turn a normal A6 into one.