And So I make use of the following for to pressure my website into maintenance mode while upgrading some things:

# MAINTENANCE-PAGE REDIRECT
<IfModule mod_rewrite.c>
 RewriteEngine on
 RewriteCond %{REMOTE_ADDR} !^23\.1\.12\.167
 RewriteCond %{REQUEST_URI} !/maintenance.html$ [NC]
 RewriteCond %{REQUEST_URI} !\.(jpe?g?|png|gif) [NC]
 RewriteRule .* /maintenance.html [R=302,L]
</IfModule>

It has labored well, however I've the problem much more maintenance mode that If only to exclude certain dir's from being delivered to the constant maintenance.html code and favour them display their normal contents.

So it might be something similar to:

root/
   .htaccess
    maintenance.html
    index.html
    everything.else.html
    /do_not_display_me
    /display_me_always

Unsure if this sounds like possible in the root level .htaccess or maybe I am going to need to get crafty with sub-dir .htaccess files, any assistance is appreciated.

This will get the job done. It informs Apache not to to rewrite individuals folders (making maintenance rules to become overlooked as rewrite chain won't ever achieve them).

# activate rewrite engine
RewriteEngine on

# always allow these folders
RewriteCond %{REQUEST_URI} ^/display_me_always [OR]
RewriteCond %{REQUEST_URI} ^/another_folder [OR]
RewriteCond %{REQUEST_URI} ^/even_more_folders
RewriteRule .+ - [L]

# maintenance rules
RewriteCond %{REMOTE_ADDR} !^23\.1\.12\.167
RewriteCond %{REQUEST_URI} !/maintenance.html$ [NC]
RewriteCond %{REQUEST_URI} !\.(jpe?g?|png|gif) [NC]
RewriteRule .* /maintenance.html [R=302,L]
  1. Letter situation matters, so if you want to match mixed situation spelling place NC, into [OR].
  2. You might attempt to add slash / in the finish of folder names for those who have files in root folder with similar names.