Is there a way to change or remove a template without having to start from scratch

I would like to start building landing pages for our site but since I used a template I am running into two roadblocks that are contrary to landing page best practices. 

1. The template will not allow me to removed the navigation bar from the page.  Landing page best practices suggest removing the navigation bar so the page can be focused on a specific call to action.  From what I understand when you remove the navigation bar on one page it removes if from all.
2. The template will not allow changing the header image or text contained in the header on a new page without changing it on all pages.

The only workaround I've been able to think of is to add an image in the section below the cover section and then reposition it over the templates cover image and the navigation bar.  The negative of doing this is it makes the page load slower.

Are there any other alternatives that would allow me to keep the template pages I like but free myself from the global restrictions is creates?

Additionally, if I were to start the site over without using a template will I run across the same restrictions?