Labeling Historical Customer Data by Region Changes

We have several events with the properties customerId and customerRegion. The problem here is that the customerRegion has changed, so for example, a customer that belonged to India, WA & Africa region, now it belongs to just India; however, there is a customer that belonged to India, WA & Africa and now belongs to Türkiye, West Asia & Africa, which means that they are not from India. I would like to label the historical data from the first customer as India, and from the second one as Türkiye, West Asia & Africa. I used this custom property, but it is not working, because it is changing the data on event-level, not on the dataset level: