If your license allows it, use Content Staging as Zachary mentions. If not, use import and export of that page template.
For reference, anything on the Page, Form and Properties tabs, are content related changes and will not affect any objects like templates, layouts and webpart properties. Changes on the Design tab are changes to page templates, layouts and webpart properties themselves, which are objects and do not affect content changes UNLESS you remove a webpart which was displaying or has content inside it.