Yes, the reduced offer is applied to any and all offers you received from the University of Birmingham. So, if you apply to three courses, and get offers from two of them, you will receive a reduced offer for both courses. However, when you make your firm and insurance choice on UCAS, you will only keep the reduced offer for your firm choice course and for your insurance choice course you will only have the standard offer remaining.
For example, if you apply for both Medicine and Biomedical Sciences at UoB and receive an offer for both, you will have a reduced offer for both appear on your UCAS track alongside the standard offer. Then, if you choose to put Medicine as your firm choice and Biomedical Sciences as your insurance choice, the reduced offer for Biomedical Sciences will be lost, but you’ll still have it for Medicine.