If you try to put on a CRX bumper onto a hatchback, it will bulge out on the corners. They were designed to match up to different fenders.

You may be able to bolt it on there, but it will look like ass....

Also, the WW CRX bumper was designed differently than the one for the Civic hatch, since the CRX did not have a filler plate on the front/rear as the hatch does.