The mis-representation of Vehicle Registration Marks VRM'S is an offence. it makes it difficult for witnesses to properly identify a vehicle from a jumbled set of characters and digits which deviates from the standard number plate layout.
Some years ago in Police Review, a traffic sergeant wrote an article in which he put forward the theory that people who altered their VRM to represent a name or word which altered the plate from its original appearance/intended use were low level criminals.
He argued that they were basically people who thought that vehicle registration law did not apply to them, he further argued that if they had little or no regard for such a simple/basic law that they were more likely to be offending in other ways.
I have to say I agree.
That said I do have my initials on my number plate, but the plate is not altered in any way, it is as the DVLA intended it to be displayed, a single character followed by two digits and three further characters.