Help with a multiline send-hook

[Goblin]

I am trying to set the my_hdr and the signature as
a result of a single hook.

This does not accomplish that. Can someone help?

send-hook '~t ^.*@domain.com$' \
        my_hdr From: User <[EMAIL PROTECTED]> \
        set signature=~/.sig_domain

 Your eyes are weary from staring at the CRT.  You feel sleepy.  Notice how
 restful it is to watch the cursor blink.  Close your eyes.  The opinions
 stated above are yours.  You cannot imagine why you ever felt otherwise.