Hmmmm ... can't run old software forever ... liken that to attempting to use Windows 95 or MacOS 7. It's all about keeping up with latest and greatest, isn't it?
Running anything like APC or Zend Opcache? Might consider clearing those caches before updating/upgrading.
From what I've read/experienced, any item in mdl_config table can be set in config.php.
One of those is theme.
Add by the 'name' seen in the table and adding a line: $CFG->[name]='value';
Example:
$CFG->theme='[oneofthe19themenames];
When it comes to theme names, they are the directories you see in the themes directory.
Sometimes one does have to sleuth 'value', however, IF the item is currently 'no value' in the table.
Adding an item to config.php does not require restart of apache - takes affect next session/click for all users. And, when one is done, one can leave the addition in-active by commenting it out ... place // in front of the line you added.
As far as updating/upgrading ... IF one installs initially via git, updating/upgrading is not that scary and easy to script into bash. One major advantage ... takes the browser and apache out of the equation (no time out issues if one uses nohup). Scripts for are located in moodlecode/admin/cli/ and are commented. Easy to follow ... and like I said, easy to put into a bash script that could do it all ... DB dump, tar ball of current code directory (date/time stamped), 'pull' the new code (which updates only the files needed) and then run the command line 'upgrade.php' script. Doesn't have a 'progress bar' but does report it's progress with 'success' lines.
'spirit of sharing', Ken