Combining \layout variables

[Trevor Daniels]

Multiple layout blocks can be combined in sensible ways, with later definitions 
taking precedence over earlier ones on an item by item basis, but the same is 
not true when layout blocks are assigned to variables.  See 
http://www.lilypond.org/doc/v2.19/Documentation/notation/the-layout-block

What I would like to do is to combine two layout blocks contained in variables 
in the same way as layout blocks at top level are combined, item by item, but 
it seems this is not possible, at least I haven't been able to achieve it.  Is 
this indeed not possible?

Trevor