Opinions about the usefulness of these mods vary. Some folks will swear by them. Other quite reputable people who have nothing to gain by it will say that if you A/B them you can't hear any difference.
Part of the problem is that some of these "hot-rod" packages like Keeley's include some component *value* changes that will make an audible difference, in addition to some component *type* changes that probably don't. After a few weeks away, people get their pedal back and they mistakenly attribute whatever change they believe they hear (some of which is *real* change, some of which is auditory memory errors) to *everything* that was done to the pedal.
There are certainly things that can be done to many pedals to reduce noise, like chip changes and resistor changes. One per cent resistors cost a bit more, and so does working out a system for using 1% where it counts and using 5% elsewhere, so many larger manufacturers just use 5% everywhere. Sticking a few select 1% components in the front end can sometimes help a lot; especially when lots of gain is applied elsewhere in the circuit. Many other things that are known to have a beneficial effect on sound in audio systems requiring very wide bandwidth and the capability to keep the appropriate phase relationships between the harmonics and fundamentals of many different sound sources (like you would expect from something that lets you hear an entire drum kit and acoustic guitar *clearly*) simpy have no benefit when processing a single instrument signal headed for an amplifier we *know* will distort and color at least a little bit.
Like most stompbox compressors, the CS-2 has a sort of one-size-fits-all rectifier circuit, which is good but may not be exactly what a particular musician with a particular instrument and playing style needs. THAT can be changed somewhat.
The CS-2 is more or less the same thing as an MXR Dynacomp and Ross compressor, with a few differences, like the OTA chip used (Roland's higher quality custom BA662 instead of the CA3080 used in the others), the variable attack/recovery control, and the input and output buffers to accommodate the FET switching. This means that many mods for the MXR/Ross units will merge nicely with the CS-2 and vice versa.
One of the mods to the MXR/Ross I have suggested that seems to have been favourably received is one to restore brightness (most compressors seem to rob the signal of high end snap). It can be easily done on the CS-2 as well. Just ahead of the volume control on the CS-2 are a cap and resistor marked C4 and R3. R3 is a 10k resistor just about dead center at the control-wire end of the board. If you put a small value cap in parallel with R3 it will provide a small, but noticeable boost to high end. Use your judgment to decide what appeals to you most, but a good place to start might be .01uf. The ideal version might well be a cap and variable resistor straddling the C4/R3 junction and the wiper of the volume pot, bt that starts to get complicated and involves machining and finding a spot for things. This mod is much easier to do. If you have a nice small, flat component, you can probably even just pop the back of the pedal, identify the PCB traces, strum, with your guitar plugged in, and keep exchanging caps (by touching their leads to the pads) until you find a value whose tone you like.
