I understand you question, but you didn't provide any answers to my previous comment.
Your walls - are they sprite object or tilemap object?
If the wall is sprite, you can create another frame for metal wall and an instance variable "wallType".
For rock walls set animationFrame=0 and wallType=rock
For metal walls set animationFrame=1 and wallType=metal
When player collides with the wall, add another sub-event to compare wallType. If wallType="rock", then enable wall jump. If wallType="metal", don't enable wall jump.
With tilemap it can be a little trickier.