I had my ECU for a 6C18 Euro V optimized here. The results were good, reduced fuel consumption and more power.

There is also Markus Gruse from "offroad-motorhomes" here in Germany who has done some ECU modifications in the past and also offers customers a OBD diagnostics kit which allows him to provide remote assistance.

In another context, I read about Piasini Engineering, who describe themselves as “world leaders in electronic and mechanical vehicle optimization.” I sent an inquiry if they can do some work on the 6C18 ECU, they might be easier to get to from Spain as they reside in northern Italy.

Due to the safeguarding mechanisms the manufacturers (have to) put in place (see regulation (EU) 2017/1151, (EC) 715/2007 for light vehicles, (EC) 595/2009 for heavy-duty vehicles) from conversations with several people and research it might even differ within a model year if an ECU modification is possible. The older your vehicle and its ECU is, the better the chances are that a modification is possible.

Best Regards

Paul