I doubt if you would get much tension on the spinnaker halyard. So the luff on the jib would tend to sag, performance to windward would therefore be poor. Sailing off the wind would be okay.
I would guess that changing the genoa for jib single-handed might be quite a challenging operation.
All things considered, if you have started out with full sail and need to reduce, you would probably be best to reef the main and furl the genoa away and not bother with a headsail.
The other alternative is to start out with a jib and full main. That would be my choice. Weather helm will be an issue if the breeze is at the top end of F3 – in which case just put a reef in.