I've got a website with a few areas which use https, however I am getting problems altering a couple of https web addresses to http ones. This is exactly what I want:

change this url url

https://www.domain.com/somefile.php?PossibleGetParameters

for this:

http://www.domain.com/somefile.php?PossibleGetParameters

This is exactly what I've on my small .htaccess:

RewriteCond %{HTTPS} on
RewriteCond %{REQUEST_URI} !^(/somefile.php)
RewriteRule ^(.*)$ http://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

With this particular condition all https web addresses are converted into http, and that i only want this specific someone to change. Can there be in whatever way to repair this?

Sure ... just take away the exclamation mark ! from second condition -- for the reason that position it negates the rule.

The ultimate rule is going to be:

RewriteCond %{HTTPS} on
RewriteCond %{REQUEST_URI} ^/somefile.php
RewriteRule .* http://%{HTTP_HOST}%{REQUEST_URI} [R=301,L]

I have simplified the rule a small bit (since you need it for any single URL only).

This rule might not work immediately as modern browsers do cache 301 redirects .. so browser may remember your previous attempts. Therefore obvious browser caches and restart it before testing the rule (or try another browser).