Can I insert any chord into Hookpad?

Ryan’s answer:

Hookpad prioritizes writing songs by chord function rather than by chord name. This function is based on music theory principles, and is not specific to any genre of music. This system shows you the structure of your song, and allows you to write music using music theory principles. However, if you are looking for certain chords by name, and not by function, you may have a difficult time finding them (since their function may be complicated). Additionally, not all chords are available in a given key (although most are).

This Hooktheory Forum post is also related: Customizing chord progressions