>Have we successfully altered the course of a major body in space with this technology? Thus, it has never been tested.

The "technology" in question is gravitational attraction. I would say it is successfully tested.

>I dont know if any of these will successfully work.

Sure. Let's just ignore the 8000 satellites in earth orbit and the 400+ planetary and deep space probes.

>The fuel required to launch it,

Titan IV launcher. 25 t to LEO. 350 million USD.
~90 kg of Xenon per engine per year. For a 30 engine configuration and a 5 year mission this will cost ~16 million USD.

>waiting for the appropriate launch window,

Launch window could be tricky, but one would still know it years in advance. And as soon as a spacecraft can travel under continuous acceleration it is no longer bound to only a handfull of low energy transfer orbits anyway.

>[..]test out the Ion engine for the first time in space[...]

I specifically chose an existing ion engine that has already been put to use.
http://nmp.jpl.nasa.gov/ds1/