Ah, remapped ECU's. I've tried veg on a remapped ECU and it smoked quite a lot so I took the remap off, then it was fine. I've often thought and questioned......... If it is possible to get extra power and economy from a manufacturers engine then why doesn't the manufacturer map them to achieve this. After all with better bhp, 0-60 and MPG figures they would sell more cars. The most common reason I've heard as well as emissions legislation and marketing slot are redundancy. Manufacturers have to account for environments in other countries your car is never likely to experience including -20C, +50C, poor servicing, substandard fuel. Remaps take advantage of this by narrowing the required operating window to extract better performance. For example I had a BMW 530D which I remapped and it was much better for it, until I took it on a skiing trip and drove it at high altitude where it was absolutely rubbish, barely got up the mountain. Back down the mountain and it was fine again. Obviously Veg oil, even when it is hot, is substandard fuel and as such the narrower window that a remap exploits might not be conducive to clean burning.
I'm not scare mongering here saying it will instantly break your engine or tosh like that. As from my experience, the most likely immediate outcome will probably be more smoke than you are comfortable with when you boot it. Over a longer period excess smoke will likely clog up the variable vanes on the TDI90's turbo.
When installing your kit use every method you can to get that veg as hot as possible:
keep the path from the heat exchanger to the tandem pump as short as possible.
Insulate the filter, heat exchanger and hot fuel lines.
If/when you are confident you will not run the car on neat diesel again you could even bypass the fuel cooler.
Adding about 20% diesel to your veg will likely improve matters, especially for the MOT.
Let me know how it runs on veg with the map, hopefully all will be well.
Trevor