Hi there,
Thank you for reaching out to us.
Changing the package name of your app (after having it registered on your AdMob account already) is not recommended, as it may disable ad unit IDs, as well as introduce incorrect reporting of ad metrics in your AdMob account. Having the same ad unit IDs across different apps is likewise not recommended for the same reasons above. I would recommend having a set of different and unique ad unit IDs for each of your apps instead.
Regards,
Ziv Yves Sanchez
Mobile Ads SDK Team