ask youself - can you bear to handle it ?
There was apost in the South West forum a few months ago by someone who had several Bass in the Taw or Torridge estuary using well-past-it squid .
Bass are one of those species which sometimes go for a really stinky bait. Dabs are another.
Unfortunately squid goes soft when it is really off (in fact it goes to jelly/liquid eventually) so you could find it awkward to bait up with it. You may want to use bait cotton (and maybe even wear rubber gloves while baiting up ! and hold it downwind of yourself)
Pink (slightly off) squid is know to be not-very-good for Cod (and most other species) but really rank squid may be good . . . sometimes . . . for some species.
If you have some left over bait from a trip and no room in a freezer (or it has already completely thawed) you can bait up a trace while it is still "fresh" and then leave it in a plastic bag to go really high. Just clip the trace on and get ready to cast before pulling the plastic bag off. and take a quick look to make sure the hook hasn't gone rusty !
OH, and don't leave stinky plastic bags on the beach just because they are not nice to take home again.