...take a look at the Librarian Dreadnought model. It is included in a kit that has 3 sarcophagus options, each of which has Blood Angels iconography directly sculpted onto them. You can't leave off the BA bits of a Librarian Dreadnought, without buying both a Librarian Dreadnought and plain one, and using just the force-weapon arm of the Librarian Dreadnought on the standard one. You're now left over with your choice of a Dreadnought with a death mask and Blood Angel iconography, a dreadnought with just Blood Angel iconography, or a dreadnought with a skull head and both Death Company and Blood Angel iconography.
It's not like you can't trim the BA icon off of the libby sarcophagus and the back plate if it really bothers you that much, it's just plastic.
For that matter, if you don't trust your hobby skills that far there's nothing stopping you from just painting it in whatever scheme you did the rest of your army and not sweating it.
You're right, you could, but it goes against GW's policy of having out-of-the-box ready models for each unit. They don't want to say "ok, now to use this model you'll have to cut away and file down all this detailing specific to other Chapters". You could also have units that need to be entirely scratch-built to have a model, but ever since the ChapterHouse lawsuit, GW proper aren't releasing any units that don't have specific models for them.