For example, I'm going to a wrecking yard to find a window, but all the websites I've found while doing a search on how to do it say that you need to lower the window until the screws are visible. Of course in a wrecking yard, there aren't many cars that you can do that with. So my question is how can I remove the window in the wrecking yard?

I don't know for sure, but usually the instructions assume you are just wanting to remove the window and nothing else...so you may have to disassemble some portions of the lift or guides to pull it.

If it's a power window, disengaging the lift mechanisms from the lift motor will allow you to manually lower the window too...

The other thing you could do if you were really stumped would be to use a battery and some test leads to directly power the lift motor into the position you want...