Setting default version in Poudriere

Hello,

Got a couple of rather silly question, but I can't find a definitive answer to either.

If I build PostgreSQL15-server, I get version 15.7. That is the latest version, so not unexpected.

I would like to build version 15.6. Ideally I would like to have both versions available because for the most part I want to install 15.7, but I need 15.6 at the moment.

So my questions are:
How do I configure things to have both versions available?
If that is not possible, how do I set the default to be 15.6 for now, with the intent of undoing that after my testing?

Thanks,
Pat