I've got a uk reg car that I'm going to be doing upgrades on brakes suspension etc, but I love in Spain and will register on Spanish plates when I'm finished, but laws are very difficult here with modding, so was wonderingly I can get it written on log book without having to bring car to uk?

 

in short no.

Colour, Engine capacity, fuel type and emissions groups are about all you can change.

Certainly can't have a list of modifications.