Hi Dask,
What is it that you're trying to acheive as the end result? When you say "new promotion request window," you mean the one that displays to the person initiating the promotion request, correct? If so, that window has several steps - are you looking to put the checkbox in a particular step?
I've spent lots of hours fooling with the promotion request windows, but I'm not a programmer so I would say I'm mildly familiar with a good chunk of it.
Thanks.