Can I create a custom sail component

Yes. But I doubt it is worth the effort.

docs.appian.com/.../component-plugins.html

Disabling copy/paste is an anti-pattern IMO. Gives a false sense of security as there are many workarounds.

This is specifc to pasting passwords but still might be worth reading: https://www.ncsc.gov.uk/blog-post/let-them-paste-passwords