I've moved this thread to the 450 sized heli section.
Yes...you can add a longer tail boom to a 450 sized helicopter.
Will it fly any better with the longer boom than a shorter, stock, boom.....I can't imagine that it would fly any better or worse, as long as the setup has been done correctly. Just as Tony said, if you have a good gyro and a good tail servo, the helicopter should fly exceptionally.
If you are interested in "stretching" a 450 sized helicopter, the only ones that I know of that sells parts to "stretch" a 450 is here:
480 Stretch Parts
Now, this is the only place that I've looked for and found the stretched parts. There are probably others.
Good luck buddy!