I have done it with ALL my Lipo's except the new ones, but they WILL eventually break, and I will mod them too....
There is not a lot to be concerned about when opening them up....except to be careful and consider what you are doing. I would recommend the following
Have a decent soldering iron - minimum 80Watt
Ensure you follow maintenance procedures of the iron, always clean the tip while soldering, and after.
Make sure you use the correct solder.
If you are INEXPERIENCED when it comes to soldering, develop your skills on things that cannot explode, it is a very good skill to posess and does not require anything more than some practise and guidance.
If you are under your parents guidance and roof, DONT DO THIS, ask someone else to do it for you.
The extensions for the LIPO balance leads are available at Ultimate-Heli....
Mister-e, check your ESC's BEC rating, it could be the end of your steering servo if there isnt one, and possibly your Rx.
Lipos put out a total of 8.49V when fully charged, any servo rated at 7.2V max power will get COOKED. .....