As this is a simple script, you will have to edit it with Applescript Editor in order to enter your own password and then recompile it back.
To enter your own password (needed to renice a process), edit the line containing \"your password\" and type your actual password (this may be a security issue: if you want to make the program safe, save it as an encrypted application).
To use it, save it as an Application bundle with the \'Stay Open\' option on. Add it to your login items and forget it.
This program has no Dock icon and no menus, which means that if you want to quit it, you must select its process with Activity Monitor and terminate it.