Ryan, I really don't want to experiment on my online web store as it can drastically have a bad impact on web users.

TR, Can this be done?

RewriteEngine On
RewriteCond %{REQUEST_URI} !\.
RewriteCond %{REQUEST_FILENAME}\.html -f
RewriteRule ^(.*)$ $1.html [L]

In my site all pages are in html extensions. For the best seo practice what should I do?