Can you redirect combat damage from a creature to a planeswalker after blockers are declared?

Prior to a 2010 rules change, players could redirect combat damage from an opponent to one of their planeswalkers. That rule no longer exists. Under the current Comprehensive Rules, a creature must be declared as attacking a player or a planeswalker (or a battle) at the time it is declared as an attacker — not later during the combat damage step.

CR 508.1 establishes that the active player declares which player, planeswalker, or battle each attacking creature is attacking at the start of the Declare Attackers step. Once that declaration is locked in, there is no mechanism to redirect the damage to a different target later in combat.

After blockers are declared (Declare Blockers step, CR 509), combat damage assignment is already determined by the attacker/blocker structure. The combat damage step (CR 510) simply has creatures deal their damage to whatever they are attacking or blocking — no choices about redirecting damage to planeswalkers are made at this point.

Some cards do allow changing what a creature is attacking mid-combat (e.g., effects that say 'that creature attacks [target] if able'), but absent such a specific card effect, the assignment made in the Declare Attackers step is final.

Example: Your opponent attacks you with a 4/4. You control a planeswalker. After blockers are declared, you cannot say 'send that damage to my planeswalker instead' — the 4/4 was declared as attacking you, and the damage will be dealt to you (or your blocker).