Why not use the per-skin tools and leave the 'master' skin alone? :D
Check out /cache/skin_cache/masterMap.php
To be able to edit a skin outside of the ACP, do this.
1) Create a new skin set within the ACP. It can be a 'root' skin or a 'child'. It doesn't matter. Make sure you enter a 'skin_key' which must be unique.
2) Put your board in IN_DEV mode by editing the constant in conf_global.php
3) Create a new master skin directory in /cache/skin_cache. It must be something unique, like 'master_myskin' for example.
4) Add your new 'skin_key' to the 'templates' array below.
5) Back into your ACP, go to the list of skin sets. Click on the menu icon for your new skin set and choose: 'EXPORT Templates into 'master' directory...'.
You should now be able to edit those files as you browse the board without the ACP. When you are done, simply choose 'IMPORT Templates..'.
*/ /*