Within the deck builder, items inherited from your template card will start with a grey outline and have a padlock icon on the corner when they are selected. When you press "backspace" to delete a template object, you will receive a warning in your browser.
If you decide to delete an object and want it back, you can use the "undo" feature to go back
(ctrl + Z or cmd + Z).
If it's too late to undo the change, the easiest fix is to create a new card, copy your content from the card missing the template items, and then delete that card.