You may want to apply a specific design to the "Bundles" page or "Mix and Match" page and you may need to create a new template in order not to interfere with the default template of the pages of your shop.
Here is how to do that.
1- Go to "Online store" > "Theme" > "Customize".
2- From the top menu, go to "Pages" > "Create Template".
3- Create this template based on the "Default page" and choose a name for it.
4- Go to "Online store" > "Pages" > The "Bundles" or "Mix and Match" page.
5- From the "Theme Template", choose the newly created template for the page and save.
Now you can apply the changes that you want to this template in the Shopify theme editor and stay assured that other products and pages that have a different template won't be affected.