Apply htaccess rules for all cases except a few - .htaccess

Question

I want every access to:
www.example.com/demo/action.html
to redirect to
www.example.com/demo/?section=action
Being action the variable that changes.
But, I do not want to apply that rule in a couple of cases, lets say:
www.example.com/demo/mypage1.html
www.example.com/demo/mypage2.html
For those cases I want them to load the real html pages mypage1.html and mypage2.html.
At the moment I have like 20 rules for all possible action variables. But as it doesn't seem to be ideal in terms of performance, I would rather have just the 2 special cases and a single rule for all the other cases.
This is what I have at the moment:
RewriteRule ^demo/removeUser.html$ demo/?section=removeUser [QSA]
RewriteRule ^demo/addUser.html$ demo/?section=addUser[QSA]
RewriteRule ^demo/addUser.html$ demo/?section=editUser[QSA]
RewriteRule ^demo/addUser.html$ demo/?section=comment[QSA]
... etc

Answer 1

You can keep exception at the top and then a generic rewrite rule:
RewriteEngine On
RewriteRule ^demo/(?:mypage1|mypage2)\.html$ - [L,NC]
RewriteRule ^demo/([\w-]+)\.html$ demo/?section=$1 [QSA,L,NC]
This assumes that demo/ directory has no .htaccess inside.
However if you are just looking at excluding all existing files from this rewrite then you just a single rule like this:
RewriteCond %{REQUEST_FILENAME} -f
RewriteRule ^demo/([\w-]+)\.html$ demo/?section=$1 [QSA,L,NC]