[Feature request] prefix for generated password

Alternatively you you could ask the author of cliphist (if that's still actively maintained; I get a 404 when visiting your link) to add a feature to ignore certain Apps (and maybe even some by default) as Alfred does:

By default, Alfred ignores popular password applications like the macOS Keychain Access and 1Password, so that you don't inadvertently copy a password to your clipboard. You can add more applications you want Alfred to ignore by dragging them into the Ignore Apps box. As a result, Alfred will not add any text copied in these apps into your history.