Which mod, the antenna or the cap?
antenna mod is pretty easy, just get some solid core 24awg wire (most bulk cat5 wireing is this, the retail stuff is usually stranded cat5, this is just my observation) and desolder the original wire and solder that one in. Its a 5-minute mod, no joke.
It gives you nice range plus you cna position the antenna wherever you want, allowing you to use it to fine tune weight distribution.
The car cap mod is very risky since if you cut hte wrong one, you make your car a nice little paperweight. Just be sure and if you have the right tools (smd soldering tip) you can try to remove it cleanly so you can put it back later. More than likely though you wont, so just get a set of fine wire cutters and chop it of at the solder points, being careful not to dmamge and pcb traces or any other components nearby.
This mod gives you some very nice range.
The controller cap mod, I do not recommend for racing use due to the extended range, it can mess with other folks cars in bad ways...imagine you car flying off the table onto a hard floor...breaking al your bodywork....and your 35ft from the nearest guy......and was that far cause bit controllers dont reach that far....it just sucks, and i decided to not play that game.
I do have a modded 57mhz controller, but i only did that since i had to see it for myself, but I havent taken it out of the house since.
If you ahve a multi-band, you can put the antenna from your original controllers into the multi and get more range, I do think that mod is fine for racing since all its doing is putting htat controller at about the same range as the original controllers.
Again remeber that range is dependant on the stuff around it, everyhting electronic emits some interference, and other factors can contribute to dead spots, so if you get bad range in the kitchen, try the bathroom for 5 mins to see if its any better...if it si it's environmental interference most likely. Or try in the living room, parents and significant other allowing, of course