For pending ledger transactions, any of the below attributes can be updated. For posted ledger transactions, only the metadata attribute can be updated.
Ledger Entries are immutable, meaning that for any updates on a Ledger Transaction that could affect the account balances, the existing Ledger Entries are discarded and new Ledger Entries are created. This allows you to look up which Ledger Entry contributed to a certain Ledger Account lock_version. See Verifying Prior Ledger States more more details.