You can try and craft/claim your open license creates a contractual obligation.
But unless the law is extremely clear about what is not subject to copyright or similar, and that this applies worldwide, I tend to think adding an open license, even one with conditions, probably adds more clarity than confusion. But I’d be happy to be proved wrong, and it probably depends a lot on the situation.
My semi-relevant blog post from a few years ago: Hierarchy of mechanisms for limiting copyright and copyright-like barriers to use of Public Sector Information, or More or Less Universal Government License(s).