in reply to
Re^2: Output should have multiple segments
in thread Output should have multiple segments
You should probably bring that up on the mason devel list.
It would help (me at least, fwiw) also if you elaborated on the instantiate and compute phases.
You might be able to do what you're talking about already
with Mason's so-called object-oriented techniques. For example, for altering the attributes of the <body> tag you might use a method or attribute, which can be overridden by subcomponents.