The load of a spinnaker that takes a "puff" is going to induce a significant load on the block.

The impact on the masthead extension (crane) is going to be a lot less tortional than axial with a normal "pick". If you're only picking up a couple or 300 pounds with a minor angle down to the deck, I wouldn't think a lot about a properly designed crane. If it was some Rube Goldberg attachment, then you might think about it further.

If you're willing to get hauled to the masthead on the halyard, then...

If you're looking a kedging the boat off of a grounding with "rock anchors" or something very strenous -- then you shouldn't use a spinnaker halyard from a crane or otherwise UNLESS, you have a salvage situation that you're trying to deal with and it's an emergency situation.