Scalable way to manage configuration flags

To pass set makeinfo options using a makefile, I have included
the css and split variables in my makefile.

For html there exist other makeinfo options, like --css-ref=3DURL,
--internal-links=3DFILE, --transliterate-file-names, and --node-files.

To add these as user otpions, would I similarly add a corresponding
variable for each?

ifneq ($(css),)
=09css =3D --css-include=3D$(css)
endif

ifneq ($(split),)
=09split =3D --split=3D$(split)
endif


.PHONY: split-chapter split-section split-node

split-chapter: split=3D--split=3Dchapter
split-section: split=3D--split=3Dsection
split-node: split=3D--split=3Dnode

split-chapter split-section split-node: $(hmldir)/antares.html

.SECONDEXPANSION:  # Enable second expansion of $(@D)

$(hmldir)/antares.html: $(srcs) | $$(@D)
=09makeinfo $(opts) --html $(split) -o $@ $<