Yes. Ajv allows you to use custom keywords: https://ajv.js.org/custom.html
If you're asking, "Can I alert all libraries / implementations of JSON Schema to use these custom keywords somehow?", then you're answer is no, not with draft-7, but YES with draft-8 (which is not yet published).
Even so, you'd still have to write the code for each language you wanted support for, to handle your keywords.