Change direction based on normal

I have tried multiple different things, but I just can't seem to find the solution I want.

I have this directional vector crawling up a wall.
After some length, it changes it's direction based on a random angle.

It works fine with this equation:

Code (CSharp):

1. var randomDir = (Quaternion.FromToRotation(Vector3.forward, -current.Normal) * Quaternion.AngleAxis(rng.Range(arcX, arcY), Vector3.forward)) * current.Direction;

The gif shows what the code does
White: The normal of the collider.
Red: The previous direction
Magenta: The new direction based on a random angle (-30, 30)

The problem, it only works when the normal is like Vector3.back.
Can someone help me with this? How can I make it work when the normal is Vector3.up for example?

 

I'm not sure I 100% grasp your question, but you can produce an arbitrary rotation around an arbitrary axis with this:

https://docs.unity3d.com/ScriptReference/Quaternion.AngleAxis.html

From that, you can change any other orientation by multiplying it by the above-created Quaternion.

I know that's super-general, but if you have a normal, that could perhaps be the axis you want to rotate some random amount around, and you would use that, then modify your other orientation by it.

 

I was overthinking the solution.
As you can see from the line of code I was using, it uses a lot of different functions.
While this line of code does the trick

Code (CSharp):

1. var randomDir = Quaternion.AngleAxis(rng.Range(arcX, arcY), -current.Normal) * current.Direction;