OK , been researching this with the help of a friendly remapping company in the UK.
My advisor said that it was possible to do the 159/Brera diesels but, suggested caution as the equipment was about £3000-4000 to do this professionally and cheaper 'clones' could
be less reliable. Worse case scenario is that if you screw up your ECU then you would need to send it to a good remapping service to get them to recover it.
To remap DIY you would need a 'Galletto 1260' device costing between $75 (delivered from the US) and £120 (plus delivery from the UK). This unit will connect to, read and finally write your ECU map but, will not act as a ODB-II diagnostic so another device would be needed to check engine faults and reset them etc..
I won't name the company or person that assisted me on this (in case his comments were 'off the record') but, once you have dumped your ECU code you can send it to such a company and expect to pay about £150 for them to use it as the basis for your remapped code. They could then send it back to you via email (I would suggest both you and they use an MD5 hashed zip to confirm no corruptions) and you can flash it onto the car. Should the worst happen and you screw up the flash (the reading of the code is 100% safe) then you would need to mail the entire ECU to such a company who could then recover it and flash the remapped code onto it before returning it to you which would cost about £300 (less the £150 you already paid for the code
Hope this all helps for anyone in my possition who wants to use such a remapping service but are just way to far away from such remappers. I would add that this sort of DIY task is not that differcult from my past experiences of playing with my GTOs ECU but does require the same level of 'competence' as say a DIY PC computer builder to be confident (i.e if you are competent to open up your PC and change the CPU and GPX card then you should be OK with this