You can use the data from grey cells without rerunning them by directly copying and pasting the correct value into the "response" column. This allows you to preserve and use the existing data without triggering a rerun of the cell.
For 50,000 rows with grey cells, you can use bulk run options instead of manual copying. Right-click the column and select Run All Rows that haven't run or have errors to process only the grey cells that need data.
Alternatively, you can use Run Starting from a Specific Row to target specific sections of your data by specifying the number of rows and starting row.
These options will preserve existing data while only processing the grey cells that need values.