you need high bend handlebars, suspension, and cutouts on your side panels. those are the white (stock) covers on the sides of your air filter. then fabricate bars that you can hold or just hold the seat. in this case, you should shave down the foam seat and replace the cover. i would also recommend cutting down the back fender so that it is shorter and does not get in the way of any tricks.
A slight change in the body style is not it. The 2001 bike was a great bike with a 6 speed gearbox and a very useable powerband. The 2002 was a 5 speed that didn't work with the yz 125s power and would bog and acceleration was alot slower. Those are the major changes that make the 2002-2004 yz125s alot worse bike then 96-01 and 05-now.
the parts that provide the power to make it move forward.
Dirt Bike riders, the state (From tax revenue) and the aftermarket companies that make parts for the bikes.
if you want it to go faster with no performance parts you will need a lighter person
Sure you can, you can buy all the parts separately and then assemble them. But it will be more expensive than buying a complete bike.
the banjo bike is not possible to make as soon as you turn a wheel it will not work and if it does work it will not remain stable
In general trying to lighten a bicycle isn't particularly cost effective. Bike parts are much more expensive bought piecemeal than bought as a complete bike. But is you insist the best way to go about is is to dissassemble your bike, weigh the parts (seat post, saddle, cranks, forks etc etc) and then replace them one by one with lighter parts.
Bike parts are well stocked at Toys-R-Us and Walmart. Finding a chain might require one to got to a specialty bike shop, when trained individuals can make sure that the right chain is purchased and safely put on.
Just don't think about it too much. Just as soon as you reach the end of the turn twist the throttle all the way (shift if needed) and you will make it over. I ride a yz125 (most underpowered big motocross bike) All jumps are small enough for every bike to take. Unless its laracco's leap at Red Bud.
Not just 125...Any bike in general. However not all parts, and even those that do, usually don't add all that much. However, if you have lots of money and can find good parts you can add about a third of the current power to your bike.
It's unclear if you're talking about weight or light here. To get a bike that doesn't weigh much you really have to start from scratch and only use light parts all the way through. Trying to make a bike lighter by replacing parts after it's already assembled tends to get pricey and still not get you that far. If you're talking about building a lamp for your bike, well your imagination is your limit. Tape a flaslight to your bars, fit a 12V battery and an acessory light from a car to your bike....
Bicycle parts are very rarely specific to a certain make & model. Functionally identical replacement parts will be available from almost any bicycle shop.