The Smoke blockchain is censor-resilient. Every 3 seconds witnesses produce a new block. Once 15 witnesses have synced that block on their server, the block has achieved so-called consensus.

Once a block has reached consensus it can not be changed anymore and is thus immutable.

This prevents that anybody could later tamper with the ledger and change the records. 

No, once a block has achieved consensus it becomes immutable. The only way to remove the content of that block would be for the witnesses to decide to roll back the blockchain’s records up to the block before the one containing the content which one wants to remove.

That would mean that everything submitted to the blockchain after that one block would be removed from the blockchain and history would be changed. This could lead to total new wallet balances, account disappearing because their creation happened after that block and thus they don’t exist anymore, and all posts submitted would be lost as well.

Thus it is highly unlikely that witnesses will decide to revert the chain and change history in order to remove one transaction. It would also require a super majority to approve of such operation (17 witnesses out 20 in the Top 20).