By law no unfortunatly.. But I have similar spacing, my numberplate is legally T3 XTJ But I have the spacing set T3XT J Nobody really says anything on it and if they do its a 30 quid fine, but to be honest I think police have better things to do than to mess about with a ruler on spacing.
You can have square on back and normal at front, If you make the square at the back different spacing than at the front you are more likely to be noticed as incorrect spacing. Id do the spacing the same front and back with it done to your liking that way you stand better chance of not getting caught. And if you are its a slap on the wrist and small fine. Just have spares in the Boot of correct spacing and you might not get fined, just say you have not changed over yet
Its a 1000 pounds fine if you are continuously caught and told and recorded on regular basis to change over