Well, I managed to ask someone I knew of who works at a modeling agency and she advised that I just wait until my extensions come out and that I wear my natural hair to the castings. That's pretty much what I figured was the answer but it would have been nice to not have to put all that on hold until I can take the extensions out. Oh, well.
She did make a great point though by saying that there may not be enough time during the open call for me to explain about my extensions and it could cause a lot of unnecessary confusion. Makes sense!