Option to make "Custom Address" permanent

[TomBarkas]

I always use a custom address and have to type it in each time. Could there not be an option to make this the default if wished?

[Jon]

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[天王寺屋]

Alternatives in the current situation (using addons.thunderbird.net)
Signature Switch
https://addons.thunderbird.net/en-US/thunderbird/addon/signature-switch/
Identity Chooser
https://addons.thunderbird.net/en-US/thunderbird/addon/identity-chooser/
Correct identity
https://addons.thunderbird.net/en-US/thunderbird/addon/correct-identity/