transaction malleability "attack" vectors
Point (6) does not eliminate this source of malleability. Rather, point (2) of BIP62 disallows all three modifications you suggested. BIP62 describes the problem:


  Non-push operations in scriptSig Any sequence of script operations in scriptSig that results in the intended data pushes, but is not just a push of that data, results in an alternative transaction with the same validity.


And the proposed solution:


  Non-push operations in scriptSig Only data pushes are allowed in scriptSig. Evaluating any other operation makes the script evaluate to false. See reference: Push operators.