Hi -- so did you publish the changed form with a new name or to a new location? If you open your xml with a text editor, you'll see an href attribute like:
href="file:///C:\Folder\TestForm.xsn"
You can change that to point to your new template. If the data structure is the same, your xml file should open correctly with the new form. Ummmm, do be sure to make a copy of your xml before changing that, okay?