The limits of reusing a decommissioned carrier

Could decommissioned carriers be reused as decoys, barriers, or sea bases?

They might be useful in limited roles, but their remaining systems and structural condition are decisive.

The response treats a retired carrier as a whole system rather than an empty flight deck. A helicopter base or other sea-basing role might be possible if the deck can still carry the intended aircraft. The hull and machinery must also remain sound enough to move or survive at sea. Power generation, communications, lift hydraulics, workshops, and accommodation all have to function for the ship to support sustained operations. The long dependency list explains why an apparently cheap conversion can approach the cost and complexity of restoring a warship.