A Variable Keystroke is a way to refer to a Key Combination like "F1", by the name of something it does in the game instead, like "Target Self"
This page covers some common modifications to ISBoxer's base configuration, including setting up custom Hotkeys and methods of Window SwitchingAny Game Video FX Window Layouts Variable Keystrokes Key Maps
Yes, it's possible! Alge's guide explains how follow and assist can be set up in EQ1.EverQuest ISBoxer Configuration Variable Keystrokes
MiRai demonstrates how to use the Variable Keystrokes feature of ISBoxer to follow, assist, and target any character from any window in almost any game.Any Game Gameplay ISBoxer Configuration Variable Keystrokes
A more game specific use of the variable keystroke feature as it would apply to a fellowship in LOTRO where team members will select the current active character and follow / assist as needed.Lord of the Rings Online ISBoxer Configuration Variable Keystrokes
The Variable Keystrokes page on ISBoxer's wiki describes Variable Keystrokes, which essentially link your game's Key Bindings into ISBoxer, and how to use themAny Game ISBoxer Configuration Variable Keystrokes