- Openerp modules:
Choose the receipt report (pos.receipt) and click on the option "Upload the modified report"
Locate the file on your hard disc and update on Openerp. After this you can try to print the pos receipt and it will come out already with the changes.
You can find more info here, regarding the openerp report mechanism.
See also: How to edit Openerp Sales Order report/template, report_openoffice: OpenOffice.org reporting engine for OpenERP