Newbie looking for a CSL

[olly22n]

Hi guys, long time BMW fan here and hoping to get into a CSL.

I have seen an AUC car which seems to add up in the right areas, only one concern for me is the after market exhaust, a cat back system.

First question is will this affect the warranty at all, ie, engine, box etc etc

Secondly, is it (well i know it will be, just how much!) expensive to go back to standard?

Thanks in advance!