Yes. there's no reason that every layout you place in a file is required to be functional to a user.
I seem to recall that somewhere someone had a file that had a single layout that had every type of object from a default filemaker theme on it. Sort of a prototype for developing your own theme and being able to copy and paste all of that. Not sure where that was but can't seem to find it now.
Anyways, once you're done getting your parts and objects to your spec, save everything as a new theme, then anyone can choose that theme on their layout in the same file and inherit all of the styling.
It still is possible to make your own custom theme by duplicating one of the embedded theme folders in the filemaker pro package contents and manipulating the CSS. This is highly unsupported and hackish though, not to mention that you'd have to copy that custom folder to ALL instances of filemaker pro that will be using it.
It's possible that Stylo already does everything that you're looking for. It also looks like development of that product hasn't really continued since August 2014 (probably due to low demand), so you may want to reach out to that developer to help him work on a newer version of his product.