Strategy for extending|augmenting an existing snap with another snap

I am exploring the best way to have one snap augment the features of an existing snap. In the debian package world this effectively meant “writing new files to directories that the parent package created”, ie into a directory in /usr/lib/appfoobar. I have taken a look at the content interface, as well as the writable file systems that snaps have available to them. Wondering if anyone has encountered this situation and what if any solutions might be possible.