Try paragraph and character style sheets; What you want to do seems to
require paragraph styles that are based on others, like (in Indesign):
Style 1 helvetica bold,
Style 2 (based on style 1) helvetica light.
Now if you change the font family, the change will cascade down thru the
related styles, but the bold or light styling will remain. Problem is,
you can't base style sheets on others in Illustrator, cause it's really
not a page layout program and at least as far as typography, it's a bit
limited. But the use of style sheets will make things a lot easier, just
a few more clicks in your case.