JD_Toims - 11:33 pm on Dec 15, 2013 (gmt 0)
What Lucy24 said with a couple of additions/notes.
If it's OldFolder to new-folder those are entirely different URLs with no way to automate it.
FYP: If it's OldFolder to new-folder those are entirely different URLs with no way to automate it in the .htaccess, but you could use PHP ;)
If you simply like "html" better, then you might as well use it in the new URLs since you're changing anyway. But otherwise leave things as they are.
Or strip the stinking extension so it's not necessary to redirect in the future if the underlying technology creating the site changes -- The extension of a URL should have no impact at all on rankings.
4. What would happen with site rankings?
Best case: it won't have much of a direct impact at all.