I see two options here, one is change the translation (in the texts maintenance go to->translate) this doesn't require a standard modification but I must be aware this change will be overwritten if you apply a note/sp/etc. which involve the text object.
Another option can be modify the text directly, the advantage of this is you have control during the SPAU to keep the modifications or not.
SAP Library - Changing the SAP Standard (BC)
You can also create a custom text in the Z class and overwrite the logic where the text is called
super->redefined_method( )
* All my logic here
I did the third option when I was dealing with Window titles and worked fine 
Cheers!
Luis