Yes, a local speederbike is required to be able to change its' attributes.
I followed fred's sides tutorial and made an add-on side that consists of a modified speeder bike (I increased the health to combat speeder level). I tested that in a map, and made a ramp jump that was 50 units high - I took the jump and survived with about half damage.
I then made a fresh mod, and used the compiled side level to spawn a stunt bike in the new mod ( thanks for the tip, fred! ).
I can post the compiled side level if anyone is interested ( it's a 530kb Zip file ) and instructions. You can then add the stunt bike to your mod by copying the compiled Side folder and making a simple change to your mission lua. This method should work, but I need someone to test it. If it works, it could open up the game to all kinds of stunt bike or pod race type maps, where you can share bike mods in very small download files.
If anyone is interested, please reply in this thread.
Here's a pic of the big jump:
http://www.saturnlabs.net/The_Lab/stuntbike.htm
Regards,
Saturn5