Everything on the stack is, in logical terms, an object, which means that you can move and copy modifiers as necessary to suit your purposes. For example, you could use two different Twist modifiers to apply complex deformation to an object that would be impossible with only one. Or, because modifiers are applied sequentially, you could change the order of modifiers on the stack to experiment with the results.
Move one or more modifiers:
To select multiple modifiers, click to select one modifier, then hold down Ctrl and click to select the others. Holding down Shift selects the two modifiers you click and all modifiers in between them.
Copy one or more modifiers:
To select multiple modifiers, click to select one modifier, then hold down Ctrl and click to select the others. Holding down Shift selects the two modifiers you click and all modifiers in between them.
Copy modifiers from one object to another:
To select multiple modifiers, click to select one modifier, then hold down Ctrl and click to select the others. Holding down Shift selects the two modifiers you click and all modifiers in between them.
The modifiers from the first object are pasted above the current selection in the second object. Choose Paste Instanced to make the pasted modifiers instances of those you copied.