Mark,
I don't know if you noticed, but that button has a VB script applied to it in Mach. If you go to Operator/Edit Button Script and click on that button (in Mach), the script will open in the VB script editor. If you look at the script applied to the button on the offsets page, that same script should be applied to the copy that you placed on the main page. You may want to place a small DRO next to it with the same properties as the one on the offsets page also.
You can leave the Jog button as is and instead of copying the "set tool offset" button and resizing it (resizing it will make it hard to read because it's a bitmap button), you can add a plain button in screen4 and when you double click on it, you can put "Set Tool Offset" in the button text field and check the "VB Script Function" button. You can then copy and paste the script in Mach from the button on the offsets page to the one you placed on the main page. By making your own plain button, it can be made smaller to fit in somewhere easier. It's a good idea to close the file in Screen4 before you edit the script in Mach and then if needed reopen it to make any layout changes.
Resizing is done by changing the values in the button properties or by dragging the handles when the button is selected. It is easier to select some buttons if you turn off the background bitmap with the IMG button at the top of Screen4.
Hope this helps a bit. Keep pluggin' away at it and you'll get it.