If it is limited to two pages only then you can do it by checking the current page name and make the function to behave differently by page name like ":-
For Customer.aspx page to view the confirmation message and not for all other pages.
Ex :-
document.location.href.match(/[^\/]+$/)[0].indexOf('customer.aspx')>-1
One extra check can be added to teh code for save button click :-
Ex :
function TextChanged() {
if (Page_ClientValidate()) {
if (document.location.href.match(/[^\/]+$/)[0].indexOf('customer.aspx')>-1) {
document.getElementById('<%= btnEmpfangSave.ClientID%>').setAttribute("onClick", "return ShowPopup(this,'<%= btnYesPopup2.ClientID %>','','modaldvPopup2','<%= lnkClosePopup2.ClientID%>',1)");
}
}
}
Hope this will definitely of help to you.