After reading through IFR Focus #14 I wanted to share a ForeFlight tip.
Yes, you can use the text annotate tool and customize the background of the text box to block the underlying text
From the Plates tab of ForeFlight, open the plate and then tap the pencil to see the annotation tools. Next, tap the text tool and place it where you want the replacement. Type 680. Now, tap the color presets and select black type with a white background. After creating the text box with a background (as illustrated below), you can adjust the location with a tap and drag. You will also need to change the font size to fit the correction in the box.