MS Word allows users to attach a different template to a document. This is a useful feature for changing the 'look' of a document and changing multiple styles at once. We do this frequently in the Publications Department I run. It can be messy, as Dennis suggests, especially when there are not matching styles (i.e. style names) in the two documents.
Two ways to accomplish the same thing in Pages:
One is to open a blank document based on the desired template and copy the text into it. It's workable and effective, again, if there are matching styles in the two docments. One trick that we use in Word that avoids bringing corruption to the new file (or the 'tablecloth syndrome' - thanks Dennis) is to omit the final paragraph mark when copying from the original document.
The second method is to import styles from the desired template into the existing document and tell the dialogue box to overwrite existing styles with the imported styles rather than to rename them. (I don't have Pages on this computer and can't give you the exact terminology that Pages uses.) Again, this requires matching style names to work seamlessly.
Keep in mind that whether attaching a new template in Word or importing styles, neither of these methods affect the margins or the layout. If you want to use the margins and layout of a different template, the copy and paste method is best.
There is not much difference in the effort among these options:
Attach New Template - open template menu, browse to new template, click 'ok'. 3 steps. (choose update styles on open - 4 steps)
Copy and Paste - open new template, switch to original document, select all, copy, switch to new document, paste - 5 steps
Import styles - open format menu, select import styles, select styles, select options, click ok - 5 steps.
Good luck,
Terry