Square vs. Round during rebuild?

Are there any legality issues of converting a square air intake to a round one? Not looking for which one is better as I know that has been discussed before... Just curious as to if I am able to change one to another during rebuild?

I could see the feds taking you over the coals if you just did it unless it was called out in a specific O-320 install. Should be a simple field approval using the parts manual.