Ask PG/HN: Is it bad form to mail YC with new info about application?

We applied to YC for this cycle and yesterday, we discovered a competitor who is so close to us in name and form that we wish we had know about them earlier. We do not think their presence greatly affects our strategy, but we sure miss the chance of being able to explain that in the application. Moreover, we are worried that the non-mention of this competitor might put us in a bad light. Should we send an email explaining our position, given this context?