I tried to change my controls that way, but it didn't work. Any ideas if it is indeed possible, or I am mistaken?
That's called using a 'modifier'. Famous modifiers are Shift, Ctrl, Alt, Q, Space, and more, but of course it's down to personal preference.
In the case of what you saw, Q was the modifier and E was the added key, so you would have to press and hold Q and then press E, within a short period of time, to activate the ability.
Furthermore, you can use special hardware in order to create and use 'macros', which are essentially saved combinations of actions, that can be recorded and then used with one press of a button. For example, you can create a macro that presess 10 keys at the very same time, but you'd be able to activate that macro with only 1 button on your mouse. This is a perfect example of why limiting UI customization is a terrible idea, since hardware and third-party software give players a much more dramatic advantage.