Shuncle wrote:
In the meantime, I will try not to merge any cells I may want to split later.
Not to take this too far off topic, but the design of Numbers includes several non-reversible features (assuming "undo" is not available or would undo more than you want). For example, enter the text "March 1" in a cell preset to the text format. If you later set the cell's format to automatic, the cell data is irreversibly set to a date.
More than once, I've selected a group of cells & accidentally made changes like this, usually when the selection is larger than what shows in the document window, & only too late to use "undo" noticed what had happened. (Should you be wondering, "March 1" means something entirely different from a date in a spreadsheet used to record cues for musical events!)
So I've learned to be very careful when making any of these changes, & to backup my Numbers spreadsheets more frequently than I would other documents.