Quetion is not clear but what I understand is you want to change the customer master data such as name and when you print out the invoice the printed document has to have the new datas right?
If yes; if you are using the standart SAP print functionality it takes data from database table. In addition your invoice already sent to data base before you changed so it seems not possible. Generally we aredevelopping a print out program in our country (because of the legal needs) if you develop a print out program you can easily make correction to print out if not maybe an user exit works but not sure!
Best Regars.