Here’s a way to set some variables for your whole blog.
Create a new template module called “Blog Config” containing some code which you want set for all blog pages published by MT; for example the page layout variable:
<$mt:Var name="page_layout" value="layout-wtt"$>
Then include it at the top of every index and archive template using the following code:
<$mt:Include module="Blog Config"$>
You can now update the page_layout in one template vs having to update it in all index and archive templates.