Hung start
Technically, if you are going to do a manual start you could leave it in 'IGN' but why would you want to?
If you are going to initiate a manual start, then that is not a memory procedure so you would then have to access the relevent section in the FCOM.
If you then follow the manual start procedure /checklist you would be out of sync with the checklist if you had left it in 'IGN'.
There is no reason why you cannot start one manually and the other automatically. It depends on what caused the hung start in the first place.