I'm not a fan of earrings on babies but each to their own.

I'm more concerned about you wanting to go behind your DP's back. If I told DH that I didn't want my boys to have their ears pierced or their hair cut and he went out and did it anyway I would be utterly furious.
And asking your DP's cousin to be the fall guy is really underhand. It's not just disrespecting your DH it's also causing trouble between him and his family.