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I use 'layers' to do something similar. Once you're in the annotate mode select 'layers' [black square with a V underneath], click on the + to add another layer, click on 'layer 1 to highlight it and white out the unwanted material, click on layer 2 and add the new material. I recommend adding the new away from the white out and move it into place with the nudge tool. If you need to move a layer 2 item, go to the layers dropdown and find the layer one change with a check mark and uncheck it. you can then select the layer 2 item to modify. That's a confusing paragraph, but it should help, with a bit of experimenting.