I wish to relabel our webstore items directory, and redirect its contents, from /items/ to /Product/ using htaccess.

However , we've several individual domains (mysite.com, mysite.co.united kingdom) being able to access ezinearticles therefore the resultant htaccess code cannot specify just one destination domain for example .com

As lengthy as all domain names/vhosts make use of the same namespace, you should use exactly the same RewriteRule in most vhosts/.htaccess files:

RewriteEngine On
RewriteRule ^products/([^/\.]+.*) /Product/$1 [L]

Best of luck! Alex.