In most cases, it isn't a problem. Most people require a higher nock point for 3 under than for split. For example, I generally need a nock point of 5/8" or 3/4" for 3 under, which I determine by bare shaft testing. For some bows that were actually tillered for 3 under, I can use a 1/2" nock point. People say bows that are tillered for split are a little noisier shot 3 under. I'm so deaf I can't tell the difference. I have had the occasional bow tillered for split that I wasn't able to tune as well as I would have liked 3 under, so that is a possibility, though remote.
When buying a new bow, I order it tillered for 3 under, since that's what I shoot.