No. Slides do not automatically inherit changes that are made to templates, so as to not disturb slides that are being displayed.
This means that if you make changes to a template that a slide is based on, the slide will remain unchanged. If you want slides that use customized template, you will need to create new slides using the customized template.
Note that if you want to keep the original template and also make a new template based on it with changes, you can clone the template and edit the clone.