Hi Mike,
This is possible by using Edit Draft on your Landing Page template. You can update your Template style by editing the HTML. When you do this, however, be sure that the Classes and IDs of your mktEditable sections remain the same to ensure that content you've added to your child LPs is safe. Once you're happy with your updates, you can approve your template draft and this will create a draft of all of the LPs using this template. You can then approve them en masse from Design Studio > Landing Pages.