If someone changes some/all the endorsements in a copy of the ledger (its not a chain), in an attempt to present a "fork", those modified transactions wont validate because the hashes of the transactions will not verify against the signature.
Ahhhh, right. Ok, so there is no chain (or history) at all, just the current state? And said state is only valid if the majority of the current N node endorse it?
Close enough yes.
There is a history of states for syncing & auditing purposes, but only the current state of the ledger is referenced when appending/voting on new transactions.
If you are syncing from a historic point, say if you were offline, then your node would request the state actions you are missing, and action them to get to the same state as everyone else.
Every historic action results in a new local current state of the ledger, then you apply the next one. The actions have to be applied in sequence for you to successfully sync to the same state as everyone else because of the determinism.
If any of the presented actions cant be applied, because they were tampered with for example, your sync stops at that point until you have a state that you can apply and continue.