Will a slightly different compact spare tire size work okay?

You might try contacting the Honda folks themselves. Call regional headquarters, Customer Service. They will transfer you to their Technical department. Or try email.

I don’t know what kind of response you will get. Sometimes these desk technicians can do no better than repeat what’s in the owner’s manual or other low-powered literature.

If I had to guess, I’d say it should be perfectly OK to move a 6-cyl tire down to a 4-banger model, while it may not be prudent to use the smaller tire upward to the 6-cyl car. So you should be all right. Try a driveway test to ensure thre is no wheel rubbing on lock-to-lock turns.