How to overwrite Welcome email message while adding any user in Group OR Share Document in SharePoint 2013

Hi,

How to overwrite Welcome email message while adding any user in Group OR Share Document in SharePoint 2013?

I am able to append custom message with default one by using following approach, however not able to overwrite.

1. Check index of aclinv.aspx

2. If index is greater than 0 then setting the value in "textarea[title='E-mail body text field']")

Thanks!!