How would I ensure total grayscale in a pdf with one mouse click.

Yes, you can get this functionality from a single click button in Acrobat. There are two parts to this process, creating the Acrobat toolbar button and creating the color conversion code.

Color conversion first. There are a couple of ways to approach this.

1. In Acrobat 8, color conversion was added to the JavaScript model. It uses the colors profiles defined in "app.printColorProfiles" to convert lines, images, text, etc. into different color spaces. The script is only a few lines of code, but you need Acrobat 8.

2. Instead of converting the PDF document, print it to gray using the "doc.print()" function. This function takes the "PrintParams" object as input. This object cantains paramenter for converting colorspaces ("colorProfile" ) and for just converting to grayscale ("colorOveride"). Both of these properties were added in Acrobat 6.

Look up the "doc.colorCovertPage()" and "doc.print()" functions and thier associated parameters in the Acrobat JavaScript Refence,
http://www.adobe.com/devnet/acrobat/javascript.php

Now, for creating a toolbar button. The simple way to create a button with text on it is outlined in this article:
http://www.acrobatusers.com/tutorials/2007/10/apply_security_with_js/

If you want cool looking and easy to identify buttons with icons on them, then check out the AcroButtons plug-in.
http://www.windjack.com/products/acrobuttons.php