Can you downgrade from 7.0 to 6.9?

In years past I remember always hearing about not being able to downgrade from one major version of android to another. Is that still true, particularly with respect to iode if I want to try the 7.0 beta?

I’m not necessarily concerned about user data because I’m not yet using it as my daily driver, and I’m fine with sideloading/spflashing.