Sure, it's possible. I'm not sure it makes sense, but that's up to you.
Do you know RegEx? You could write a RegEx that extracts the HTML header and body, and adds each to the respective parts of the merged file.
You'll need these KM Actions:
- For Each action
- with a collection of Finders Selection collection;
- OR, a Folder Contents collection
- Search using Regular Expression action
- Set Variable to Text action
- Read a File action
- Write to a File action
and maybe some others, but those are the major Actions.
For a person new to KM, I'd rate your task at moderate difficulty, but it is a good task to learn on. Just give yourself plenty of time and patience. 
I, and many others here, could do this for you, but you'll learn a lot more if you do it yourself. If you really get stuck, post back and we'll help.
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@bounce, welcome to Keyboard Maestro (KM) and its Forum.
KM is one of the best Mac automation tools available, its Forum is one of the best and friendliest forums on the Internet. Whenever you reach a tough stumbling block trying to use KM, please feel free to post your question/problem here for help.
You will also find this helpful:
Tip: How Do I Get The Best Answer in the Shortest Time?
Getting Started with Keyboard Maestro
- Read the Quick Start.
- This is essential to become familiar with KM terminology
- Do the tutorial (Help ➤ Tutorial) in the KM Editor.
- Gives you a live walkthrough of creating a macro in the KM Editor
- Review/Browse the Available Macro Actions
- For Help with an Action in your Macro, click on the gear icon
at the top right of the Action, and select "Help" - Search the Keyboard Maestro Wiki for detailed help.
- Start small, and grow your macros organically.
- Be prepared for some trial and error in the beginning.
- Make good use of this Keyboard Maestro Forum
- Checkout these Great Resources
- Search for existing macros
- Post your questions/issues if you get stuck
- Be sure to first read: Tip: How Do I Get The Best Answer in the Shortest Time?
For more help, see Getting Started with Keyboard Maestro and the Forum .
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