Check out this post where I have an example of using tap_state to activate/deactive a layer when a button is clicked. You should be able to modify your expression to use tap_state to engage your drag-scroll layer (I assume Layer 1), then make a second expression that uses hold_state to engage Layer 2. However, I haven’t tried that myself.
Per that whole thread, I’ve also struggled with Reverse Polish Notation. It helps a lot to use comments (which are unfortunately not saved in HID Remapper configs).
Saying all of that, I’m not sure if you really need a second layer. Why not just do this?
- Hold 90004 = sticky left button
Then you don’t need an expression at all. You would just have to hold 90004 again to release it (instead of using 90001).