When you regenerate the code file after having added a prelude in place, the Prelude Acceptance Chooser is displayed. Adding a prelude into the Preludes dialog will not cause the Prelude Acceptance Chooser to appear.
In this dialog, you can choose individual preludes which have changed since the file was last generated and specify whether you wish to accept or reject those preludes. Select the preludes and press the arrow keys to move them from one list to the other. When you press "Ok" only those preludes you chose to accept will be regenerated. Alternatively, you can choose to reject or accept all the newly added preludes. Preludes which you reject are deleted and cannot be retrieved at a later date.
Preludes which were added before a previous code generation took place are retained - the Prelude Acceptance Chooser only affects those preludes which have been added since your code file was last generated.
Note - If you unset the "Edit in place" toggle and you have added a prelude since the last code file generation the Prelude Acceptance Chooser is displayed because any new preludes need to be shown in the Preludes dialog.
See also: