I have a Macro Group called “Template Group” with various macros that have a single action template.
I use an AppleScript to insert those “favorite actions”.
I also use @DanThomas' wonderful template manager KMFAM.
And to answer you specific question – I have a very specific AppleScript to insert my custom header.
Here's a version I've turned into a Keyboard Maestro macro:
Keyboard Maestro Editor ⇢ Paste Dated Attribution Action v6.01 Macro - #11 by ccstone
-Chris