I recently just bought a 2017 s3 saloon and was going to do a res delete but not sure if that would void the warranty or if they would argue the modification if i was to need to make a claim, any help appreciated, I’ve heard and read that it doesn’t void the warranty but would rather ask on here aswell. 

Any modification could be used as an excuse to void a warranty, whether it was justified or not.

Definitely would be classed as a mod. Be warned though most of these warranties aren't worth the paper they're written on 

2017 after-market warranty, will have more small-print than Turin treaty. Leave as it.

Did the comments above help Lewis? I know you have seen them.