iPhotos

No

What software do you have? There is no iPhotos - there is Photos version 1.5 and iPhoto version 9.6.1

What specifically do you need? You can add faces to photos - the method depends on what you actually do have

LN

If you enlarge a photo and get info you can add faces in the info window - click on the + sign to the right of faces in the info window

LN

Is there a way to force iPhotos to update the Faces collection? Running 10.11.6

No. Photos scans the faces once, when you import new photos. That scan is running in the background, when you are not working with Photos. You cannot force Photos to repeat the scan for a photo other than by deleting it and importing it again.

You are welcome

LN