Will MosModule execute its command in custom HTML module?
The answer is Yes and No.

No, all the latest version of Mambo, Joomla MiaCMS or any of the forks won't parse mambots in custom HTML module by default but there is a way!

Yes, it can! But with a special module call MosModuleMod

How you might ask?

Assuming you already install MosModule and MosModuleMod!

First you create an article that you would enter all your custom HTML module code in your article then make note of the article ID.

Then you go to your module manager look for MosModuleMod and enter to "MosModule command:"

articleid=yourarticleID

That's it!

Now your article will be running as custom HTML module in a module!