I’ve just started looking at Piranah as a way to jump start a personal project. It looks great, but I would like to extend some of the models. For example, have an physical address field for every bog post.

What is the best way to add that, without causing issues when upgrading later?

Given that you’re using the latest version of Piranha for .NET Core the content types are very flexible and you can extend them in many ways through the framework. You can find good documentation on this here:

http://piranhacms.org/docs/basics/how-to-setup-content

If you’re using the legacy version of Piranha (2.x) you can read about it here.

http://legacy.piranhacms.org/docs/extend/page-post-types

The content model of the latest version of Piranha is far more flexible.

Best regards