In civil law countries (after Brexit, 100% of EU is civil law) generally you can't change your name at will or by simply starting to use it, it usually requires

In civil law countries (after Brexit, 100% of EU is civil law) generally you can't change your name at will or by simply starting to use it, it usually requires asserting one of specific reasons that (in the eyes of the law) justify a name change, a request to authorities and their approval - which would be denied if you wanted to change your name to something that has 2^40 characters. If you did officially change your name to something interesting, I presume the bank would definitely have to accommodate it; but the restrictive part would be the process of actually changing your name.