ErichAD |
There isn't much to work with rules wise. In theory, since each template is added sequentially and not simultaneously, you'd be adding the advanced template to a creature with the advanced template and not adding the template twice. Since templates don't add bonuses, I wouldn't expect them to follow the bonus stacking restriction on bonuses from the same source.
Some templates have requirements that would prevent them from stacking with themselves, you can't add fiery template to a fire type creature for example. But advanced is pretty bare bones and doesn't have any requirements.
I'd probably limit it somehow at a table I was running, but I don't see any restrictions in the rules themselves. I could be missing something.