Thank you Anita, unfortunately affecting a "little bit" is not good enough. The customer requirement is precise and very clear: the field must have exact given width.
Since due your answer my assumption is right and there is no way to customize that one, the only way I can suggest to our customer is to download affected WDJ, decompile, build an own Z_ application based on the downloaded one and maintain it with every applied SP, patch etc. This would be a disproportionate effort for such a small change like field width, but I see no other chance. Thank you,
cheers