Actions such as deletion and restoration of Amazon EBS snapshots are possible, but direct modification is not; however, changes can be indirectly made through volume manipulation followed by creating a new snapshot. Snapshot reallocation can be accomplished by copying to different regions or accounts.
On the Amazon Web Services (AWS) platform, it is indeed possible to perform actions on an existing Amazon Elastic Block Store (EBS) Snapshot. While direct snapshot modification is not supported, you can delete snapshots that you no longer need, restore snapshots to create new volumes, and perform actions akin to snapshot reallocation by copying snapshots to other AWS regions or accounts. It's also worth noting that to modify a snapshot, you can create a new volume from it, make changes to the volume, and then create a new snapshot of the modified volume.
To summarize the options provided: Snapshot deletion (B) and snapshot restoration (C) are definitely possible. While snapshot reallocation (D) is not a direct process, similar outcomes can be achieved through copying and transferring snapshots. Snapshot modification (A) in the sense of altering the data contained within an existing snapshot is not possible; instead, changes must be made to a volume created from the snapshot, after which a new snapshot can be taken.