The gizmos to move the cables in the editor are too big/small

You can change the size of the handles in the Settings menu (GameObject->2D Object->Cable Renderer->Settings)(see Editor Settings)

Snap is enabled but handles don't snap

Hold Ctrl while dragging the handles to enable snap

I want to make my cable bigger/smaller without losing its current resolution

If you're ok with the current pixel size (thickness) of the cable and want to scale the cable up or down, simply parent it to a "container" GameObject and scale the parent.