What you have in mind is proxy editing, which is commonly used for lengthy or complex projects with high resolution files. Since Videopad caches all imported files proxies may not be needed. A project will reload quickly unless the cache has been cleared.
But when caching becomes too tedious, proxies can help. The procedure is outlined in the Proxy Editing 'sticky' above.
Sometimes it's helpful to divide lengthy projects into more manageable segments, export each and then assemble those parts for the final project.
Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. From the HOME tab, that choice is available by clicking the chevron to the right of the Save Project button on the toolbar.