ActionScript 2.0 :: Using One Variable To Write To Another

I need to have one variable contain the name of another variable so I can write the actual value using either variable.

On my main timeline I have this code:
var globalvariable = "blank";
On a movieclip I have this code:
on (press) {
var testsend = name._root.globalvariable;
testsend = "IT WORKS!";
trace(_root.globalvariable);
}

I'd like the trace to read "IT WORKS!" but it's always "blank". The reason for this is that I have a controls options page where users can change their key binding for the various controls of a game. There is a list of the actions in the game with a field for the currently assigned keyboard shortcut. When they press that field, it's a button that pops up a keyboard graphic which has buttons on it for every key. Clicking one of those buttons should assign that keyboard equivalent to the corresponding field.

So I want to have something like this actually work:
Click the MoveFowards field and click "Spacebar" on the keyboard graphic and now _root.Moveforwards has a value of "Spacebar".
Click the Jump field and click "Spacebar" on the keyboard graphic and now _root.Jump has a value of "Spacebar".
Click the Shoot field and click "Spacebar" on the keyboard graphic and now _root.Shoot has a value of "Spacebar".
So I need to pass the name of the variable to the keyboard graphic so that it outputs to the correct global variable and writes its output to the correct field.