As for your second question, it depends on what kind of platform the diamond industry builds on. If the diamonds are tracked using a smart contract on the public Ethereum chain, there may be special functions in the contract that allow certain entities to edit data in the contract. The problem with this is that consumers have to trust that the companies use this write access honestly. A partial solution might be to only allow certain data in the smart contract to be edited IF at least X number of companies in the consortium agrees to it. Still requires trust, but less of it.
If they're building their own blockchain to track the diamonds, and consensus is simply maintained by a small group of entities in the industry, then it's trivial to edit the data. But of course, if this is the case, then it begs the question of why a blockchain is even needed. Just use a shared database.
If they're building their own blockchain to track the diamonds, and consensus is simply maintained by a small group of entities in the industry, then it's trivial to edit the data. But of course, if this is the case, then it begs the question of why a blockchain is even needed. Just use a shared database.