The tone pot in the peace gun is similar to a guitar tone pot. It's a resistor in series with a cap to ground in a sidechain configuration. Basically, when the pot is turned up, the resistor dominates and all frequencies have a high-ish impedance to ground and are bled off equally. When the pot is turned down, the capacitor dominates and the high frequencies have a lower
impedance to ground than the low frequencies. So to make it permanently all the way up, option c is correct: replace the pot with a resistor of the same value. If you want even more treble, use option a, just remove it entirely.
This solution is not universal. There are many ways to wire a tone pot, and the right way to replace them with resistors depends on how it's configured, so you'll have to look at the schematic. If the pot is wired as a variable resistor: dial in your favorite value, measure the resistance and replace with that value. If it's wired as a voltage divider it will have 3 connections instead of 2. So dial in your favorite value, measure the resistance, and replace with two resistors in series such that R1 + R2 = pot value, and R1/(R1+R2) equals your favorite setting. If your favorite setting is max or min, you can get away with one resistor.
I've left out some detail here, but there are a few other threads about this, so try searching 'replacing pots' or something similar.