What power increase can be expected?
With the motor shown on this page, which was built from a Torcman TM280-15 kit, I got at least 50% more power after I modified it. Input power went up from the advertised maximum 300Watts to over 450 Watt at an efficiency of 72% with a rather big prop, which is quite a respectable number for outrunner motors (max. efficiency is 82%). When I put a datalogger in my fun-fly model, it showed that the motor does 600 Watt during full power punch-outs.

The power increase you'll get with your motor, would depend on a few things, eg. the quality of the stator laminations, the design of the motor as a whole, magnet quality, the ability to do neat and efficient windings, etc. 

What does the mod entail?
All that needs to be done is that 16 magnets should be installed in the bell and the stator needs to be rewound according to a new winding scheme.  

How do I know if my motor can be modified?
This mod can be done on any outrunner motor that has a 12-tooth stator - even on commercial motors like AXI, Hyperion, etc. However, it's necessary to remove the stator and magnets so they can be worked on.

I modified my motor while assembling the kit, therefore it wasn't necessary to struggle to remove the stator and magnets from an already built motor. When I ordered the 14-magnet kit, I also ordered 2 extra magnets - to ensure that all 16 magnets are exactly the same.