When you build software using a library, it will be linked to a specific ABI version of that library, and there's no way to change that other than rebuilding that software. So, looking at pkg certainly won't help. You'll have to rebuild all the ports using ssl to link the base OpenSSL.
A good way to do it? IMHO, always using poudriere. If you change DEFAULT_VERSIONS
, it will know itself what needs to be rebuilt.