Is there a way to conditionally change the state of a collapsible field group in admin, ie without changing a template or module file?
If you want it to be open on page creation, you can target the page using the node-add-CONTENTTYPE class on the body. Using some jQuery in document ready you can set it open.

Something like:

jQuery('body.page-node-add-&lt;YOUR-CONTENT-TYPE&gt; fieldset.#YOUR-ID-HERE').removeClass('collapsed').children('.fieldset-wrapper').show();