On my E82 135i, I was meant to take it to Sandton Auto as the head tech there knows the work done by Sportech.
I took mine to Auto Bavaria where I bought it (with the modded ecu) and told my sales guy what had been done to it - they had no problem servicing it and didn't affect the mplan at all.
I've heard of late however, they've become a lot more strict and hence the mods that are removable or allow you to restore to orig. pre service are the ones to go for