Be careful! had my bmw 320D remapped at 37K miles, turbo went at 39K , filled CAT with oil , 2 weeks out of warranty, luckily BMW coughed up!, another turbo put in, injector went at 46k, then another at 52k both £400 +, took car in for service at 60k told turbo on its way out only done 23k since replaced.
said " top it up with oil and im off to VW" hence bought a GTI.
GTI petrol not diesel so maybe better but I wouldnt mess with the original, save up and get an ED30
A full stainless steel exhuast inc down pipe and sports CAT will give around 20 bhp with no side effects.