To keep track of which cells have been edited, we change the fill color of the cell in Workbook Designer (each engineer has a specific color).  That way, others know that cell has been engineered and who did it.  When possible, we also copy the old formula off to the side for reference if needed later.  However, this isn't always feasible, if the formula is in the middle of a table with no empty space around it.

Since we generally can track WHICH cells are engineered, we'd now like to also track WHAT exactly was engineered inside them.  Depending on the formula, it could be easy or difficult to decipher this.  We've been looking at ways to imbed "comments" inside of formulas but haven't decided on a particular approach yet.  One example would be something like:

=IF("Eng"="Eng", new formula, old formula)

This way, the "Eng"="Eng" would indicate it has definitely been engineered (while always returning TRUE), and both old and new formulas would stay intact so the next user could compare them if needed.  If the next user needed to undo/change the engineering, they would clearly know which parts to delete/edit.

Does anyone else have a method they like for keeping track of what, specifically, has been engineered inside of a given formula?