Most (not all) of the 'tuners' have no grasp of how the new diesels and DPF's work as an integrated system.
Indeed what does the remap do during regeneration....? does it increase the exhaust phase injection duratio to the detriment of the DPF itself - filling it with too much fuel? - in the case of a remap - probably - in the case of a tuning box, definitely.
Also during a regeneration the surfeit of air that the tuners rely on is not present (try lifting off during a regenertaion and you will note zero boost - as the VNT is open) so youre overfuelling and making it worse.
Usual diesel tune - increase injection pulse duration and lift maximum boost, on an atmopsheric petrol car - advance the ignition - thats about it - for £300 or so.
...and people ask is my car modified! - no chance!
BTW comnmercial diesels including ships have increasingly stringent emission controls too, though urea injection (Adblue and the like) to reduce NOx is the key here, particulate emmisions arent an issue at sea, and the lower velocity of commercials on the road leads to particles that drop into the gutter in many cases.