Brenda, don't worry about it smoking a little more than you are used to, as you are probably aware i have a re map module for my alhambra and when the car is re programmed for the higher output it does tend to give out a fair bit more black smoke but only when it is working quite hard, at all other times it is just as clean as normal. you will notice the smoke a lot more when towing.
My dms module does upload a new programe to the cars ecu and i took it back to the suplier becouse of the smoke the car was tested and all was well allthough i do not think it would pass the mot when it is due so i will have to re map the car back to standard which my module allows me to do when the mot is due.
One thing i have done is to replace the cars air filter with a K & N performance filter, yes i know before any one jumps down my throat that these can cause air flow meter failures but the advantages far outweigh this minor issue, i get better air flow so less smoke (although it is still noticable)better still mpg and it has eliminated the turbo pipe calapse problem that seems to effect the tdi engine that has been modified.
Like me you have had the modification for towing not for racing around the streets so i would not worry too much unless it becomes a problem at the mot stage, if it does then just get the seat dealer who fitted the mod to mot the car, they did the work in the first place.
On another point i have taken to changing the oil in my car every 6 thousand miles due to the fact that it is modified and it spends over 50% of its time towing the engine allways seems far quieter and smoother once the oil is changed, i know at