For clarification purposes, changing the 0 in for EX in the gradebook means the exported version of the gradebook in Excel. Changing an EX to a 0 inside the Canvas Gradebook will alter and lower the grade for real. Excel ignores text cells when computing averages and sums, so it should not be necessary to change the EX there, either.
The grade might be affected by assignment group weights and drop rules. Neither the assignment group, the weights, or the drop rules appear in the exported CSV file, so computing the grade from an Excel file can be difficult.
This discussion post is outdated and has been archived. Please use the Community question forums and official documentation for the most current and accurate information.