What happens when you put a +1/+1 counter on a planeswalker?

Question

Some commander decks have Planeswalker commanders. What happens when you put a +1/+1 counter on one of them, such as with Opal Palace?

Answer 1

Non-creature permanents can have +1/+1 counters on them, they just don't do anything until the permanent becomes a creature. Say you have a man land. If you animate it, then add +1/+1 counters to it, they stay on it even when it stops being a creature.

Also, cards like Earthen Arms can put counters on any permanent. Its gatherer says:

Any permanent can have a +1/+1 counter put on it. Those counters won’t have any effect unless that permanent is or becomes a creature.

Answer 2

A +1/+1 Counter exist on the commander. It doesn't count as a loyalty counter, it doesn't increase the loyalty.

If by some facet the commander is turned into a creature, the +1/+1 counter would change its power and toughness.