Reversing the rendering process is always messy and almost as often lossy. Don’t. Keep around the data in structured storage even after you’ve used your templates to output it in rendered form.

If you set things up right on the webserver’s end, you can then switch horses at any time, even generate half the site dynamically, the other half statically. The templates can be identical – eg. the Template Toolkit tutorial shows the same template being used with tpage, then ttree, then from within a CGI script.

Just don’t throw away your structured data.

Makeshifts last the longest.