Shift the Range of the Tone Controls
This modification does not alter the appearance of your guitar.
This modification is probably the most simple modification possible -- we don't even need a schematic! Let us say, for example, that you just aren't happy with your pickups because they don't have enough high "punch." You always leave your tone controls turned up to maximum treble -- and it's still not enough. Good news! Your pickups may be fine, the tone control is probably "throwing away" some usable tone even when it is turned all the way up. Why would the manufacturers do this? There are two simple reasons. First, you may like more treble than the "average" player that the manufacturers target. Second, the manufacturers tend to use inexpensive components (caps and pots) which can vary widely in their actual value.
In any case, it is very simple and very inexpensive (about fifty cents) to shift the range of your tone controls. First, locate the tone capacitor. It should be soldered to one of the terminals of one of the tone pots. Determine what value it is (see the section on reading schematics for hints as to common tone capacitor values). To shift the tone control "up" so that you have more treble available, replace the tone capacitor with one of lower value. For example, if the existing capacitor is 0.02uf, replace it with a 0.01uf capacitor. If the existing tone capacitor is 0.033uf, try replacing it with an 0.02uf capacitor.
On the other hand, if you usually keep the tone controls all the way down, you may want to replace the tone capacitor with a slightly larger one to shift the tone range towards the bass end.
That's it! All there is to it. Easier than changing pickups, much cheaper, and certainly worth a try before you slap down a couple hundred bucks for pickups.