I'm wondering what you mean by MIDI. (1) Do you mean using controller messages? (2)or do you mean pressing buttons or moving sliders?
[This first part may be of no interest to you at all; sorry; I was just unsure what you meant]
(1) Rolands SoundCanvas series allowed you to control some paramaters on individual drum hits (e.g., a single snare or cymbal or something) using CC98, 99, and 6, but I don't think that was implemented on the JV/XP series. And even then, the only parameters you could control were coarse tune, level, kpan, reverb send, chorus send; I don't think you could tweak filter cutoff or resonance).
On the JV/XP series CC71 controls resonance (TVF), CC72 decay time (TVA), CC 73 attack time (TVA), and CC74 Cutoff (TVF). I know you can control Tone Level using CC 80, 81, 82, 83, and CC101/100/6 can control coarse or fine tuning per patch depending on the value of CC100.
So what does this mean to you in rhythm mode?
CC99/98/6 were used on the SoundCanvas to control Filter Cutoff and Resonance. The problem with the JV/XP series is that there is no way to stipulate rhythm instrument (key) number. On the SoundCanvas, CC99 on channel 10 stipulated parameter (level, pan, etc.) and CC99 stipulated rhythm instrument (note in the rhythm kit). CC6 was the amount of change.
So you could try that on your JV/XP on channel ten, but I don't think it works. For some reason, Roland seems not to have implemented this on the JV/XP series.
More likely:
(2) To do it by pressing buttons, you'll be using sysex. In rhythm mode, go to the instrument you want (e.g., a cymbal) and go into its editing screen. With (a) Transmit Edit on and (b) your sequencer recording on an empty track, try pressing the button of whichever parameter you're trying to edit in real time. The sysex you're generating should be recorded into your sequencer. When you play it back, it should tweak that rhythm instrument just the way you did while recording.
I've never done this, but in principle it should work.
The problem you may run into is that you're probably going to be generating a lot of sysex, which may result in some MIDI slop or latency. If it does indeed work, go back and THIN that data several times until you get the effect you want with the greatest amount of thinning (i.e., with the fewest sysex messages).
Again, I've not tried this, but I think it should work.
I don't think you can use the sound palette; notice that the lights don't go on when you're in rhythm mode. Bummer.
Good luck.