Identifying microcontroller ic (54281)
As Brian Dummond said in the comments, it's probably not even a microcontroller. 

You might want to use and logic analyser / oscilloscope to monitor its ins and out, and reverse engineer it. 
You would also have to try and make a circuit diagram, as Bradman175 said.

This label seems to be only a part number and not an actual reference. We couldn't tell you wich IC it is, even if it wasn't custom.

EDIT : this seems to me like the helicopter is a remote controlled helicopter, probably infra-red so I'd say the IC is a custom IC that decodes the IR signal and drives the motors accordingly. What do you think if when saying "modify it"? I don't think there's much to do except removing all the card and keeping just the electro-mechanics (ie the battery, the motor, the wings...) to add your own command electronics.