PS: 2

A solution for all, but only the text or the HTML code of pages site (for
change extensions by group , exist other software), but a few hard, because
was renew each time.... that you updated the site... 
If you have Dreamveawer (Adobe, ex Macromedia) HTML editor (but this fonction
exist surely in other software of this type). 
In "edition" menu, you choice "search and replace", then choice the folder of
your site, then choice "source code" and type the old text or code (.shtml)
and the new (.html) and launch