Can you assign combat damage to a planeswalker instead of its controller without the creature attacking the planeswalker directly?

When you declare attackers, each attacking creature must be assigned to attack either a player, a planeswalker that player controls, or a battle that player protects (CR 508.1). This choice is locked in at that moment — you cannot redirect combat damage from a player to their planeswalker after attackers are declared.

During the combat damage step, each attacking creature deals its damage to the object or player it was declared as attacking (CR 510.1). A creature attacking a player cannot split or redirect its combat damage to a planeswalker that player controls instead.

This is a common misconception left over from an older rules era. Prior to the 2010 rules update, players could redirect combat damage from themselves to their planeswalkers. That rule no longer exists — now the attacker must target the planeswalker directly at declaration (CR 306.7 covers planeswalkers as attack targets).

Example: Your opponent controls Liliana Vess and has 10 life. You attack with a 5/5 creature targeting your opponent (the player). Even if your opponent's life total doesn't matter to you, that 5/5 will deal its 5 damage to the opponent's life total — not to Liliana — because you didn't declare it as attacking Liliana during the declare attackers step.

If you want combat damage on a planeswalker, you must declare the creature as attacking that planeswalker when attackers are declared. You cannot change this assignment later in the combat phase.