there are different options possible from my point of view:
You could try to change every export mapping in the ruleset from "./mods:mods/..." to "./mods:collection/mods:mods/...". We did not test this, though.
Another solution could be that you use the default export mechanism and add an automatic step with an XSLT transformation afterwards. This will work but you need to be aware, that after clicking the export icon (globe) you need to run the other step, too. Not very user friendly in case of manual changes and probably quite error-prone…
You could use the goobi-plugin-step-exportPackage plugin and call the XSLT there. As this is a step plugin you need to be aware, that this does not have an effect to the globe icon, too. If it is the only export step in the workflow you won’t see the globe, too. This makes it less error-prone but not very user friendly, too.
We develop an extension to the default export mechanism to call an optional XSLT transformation. If you are interested in this development feel free to contact us to clarify further things.