There is a long available feature to "disable" keys in GnuPG. This deactivates the local certificate for regular use. Kleopatra should respect this as well:
- In certificate view show "disabled" (de: "inaktiv") in the "User-IDs" column.
- In certificate view add "disable" or "enable" in the context menu.
- In "Details" view add "disabled" in bold next to "Valid until" in case it is disabled.
- When searching for certificates in "Encrypt for" fields, don't show disabled keys in the drop-down menu.
And either:
- make a filter showing "disabled certificates".
- don't show disabled certificates in any of the others filters.
or
- make a toggle to show/hide "disabled certificates" everywhere
Info: The "disabled" status is stored in the trust-DB. It can be changed with "gpg -edit-key" and "disable".