Please let me know how will u make those unusable to anyone!
So I'm not an expert but this is the way I understand a hard fork...
SIGT V1 will continue running as long as there is nodes up and everything on that chain should stay the same as it is/was. I don't think they can actually burn coins on the original chain, they don't have control of it, hence the hard fork.
SIGT V2 will hard fork off of V1 which means they basically just take a copy of V1 blockchain at a certain block #. Once this is done, it's a new blockchain that has nothing to do with V1 and they can go in different directions. This allows the devs to setup a swap which is basically users getting 25% of the V1 coins they had in V2 coins.
I'm not sure of the details on how they "enforce" a swap on the new chain however.
If I'm wrong, someone please correct me.