The 14 day activation period for new A+ members doesn’t apply to ticket sharing, tickets from season ticket holders can be shared to new A+ members immediately 👍
For West Ham, membership would be needed (or purchase history) - think they are sold on the same basis as other available tickets (ie if purchase history was needed, that would still be the case for an exchange ticket etc)
Even if it’s sold out, the ticket exchange will be open so if you need a single seat there should be several available as these are more difficult for the club to shift.