Q:

Can the root user change the owner of a file that he doesn't own? 

My web server uses the user www-data to access/change files.  This causes permission issues for php file upload etc.  for files owned by root (or by any other user). 
I'd like to use the 755/644 permissions for my folders/files (rather than 775/664), so I'd like to actually change the owner of the files to www-data, rather than just the group. 
I don't want to run in to the situation where the root user can't access/modify the files though. 
I'm sure this is basic knowledge for most people, but I just wanted to double-check it.  If I change the owner:group of a file to www-data:www-data, will the root user still be able to edit/access the files?  Would the root user be able to change it back to root:root if desired? 

A:

In most situations (read default installations), root can do anything a regular user can and much more.  If you think root cannot do something, remember it can become a user who can :)
You'll be fine.