Rain Area of Spawn Customized by Blueprint

Hi guys,
I’d like to make a rain particle system which its area of spawn could be customized by blueprint. The point is to find a way to use the same particle system and procedurally customize the area where particles are spawned. (ex: rain particles are emitted from a grid and when I scale the grid, it dynamically increase/decrease the area of spawn).

Do you have any hint and/or workflow to get it?

Thank you!