This doesn't directly answer your question, because it relates to RealBand not BiaB. But since you have the Windows version, you also have RealBand, and you can load the song into RealBand, select only those bars that you want to change, and generate only those bars. Then save it again as a BiaB song format and load it back into BiaB. This might be the quickest way to achieve your desired result.

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