Tax code at change default settings page

Hi experts,

we are in SRM 7.0 , we want to set the tax code field in default settings page ,

we did the WEBDYNPRO enhancement to set the tax code drop down list in page default settings.

we need to set the selected tax code in default settings page as default tax code for all line items in the shopping cart.

experts please help.

Thanks,

Bhargava .