For the OPL instruments I had a trick that I used to use, which I guess has been considered a glitch and patched out now, unless the change has only happened to 64 bit versions of OMPT.

What used to happen as far as I have been able to make out was this:
if you adjusted the cutoff of an OPL whether in the instrument tab or in the pattern it would change the volume of the second oscillator, but it was only making that change to OPLs without the additive synth clicked. As a opl version of the cutoff it wasnt accurate to an actual cutoff, granted, but I got a lot of use out of it, creating great random variation in the OPL instruments I made. It is still working with the ZXX commands in patterns, but doesnt work with the random variation slider.

For the request I would like to propose something like this as an official part of the way opl instruments are incorporated into the effects which arent presently doing anything to opl instruments.

I know the SDX commands are applying delays as they should... the ZXX effects are still applying the 'glitch' I just talked about which is very useful, but I am sure we can find effects that are presently not being applied to OPL instruments such as the volume, reso random variation sliders, and other things in the pattern.

I propose, for both kinds of OPL, in the instrument tab :
the volume randomizer effect the volume of the whole instrument
the cutoff randomizer effects the volume of the second oscillator only (like it used to work, but now for additive opls too)
the resonance randomizer effects the volume of the first oscillator only (which would end up being a second volume randomizer I guess for the opls that dont have additive synth clicked)

In fact, maybe a whole different design for the instruments attached to OPLs would be warrented since so much of them is very different from sample instruments - and thus we could have randomisers for all the sliders in the OPL sample tab and they would be marked for what they do.

and for the effects on the pattern :
ZXX remain a way to adjust the second osc
vxx and other volume commands stay as they are obviously
HXX vibrato could switch the vibrato button on and off
IXX could switch the tremelo button on and off
OXX could apply to the attack rates of both oscillators O00-O7F would be the first osc and O80-OFF could be the second osc
QXX it would be great to get retrigger on OPLs but I am sure that obvious change has a good reason for not being in OMPT yet

These are just some ideas, and I am sure you guys can figure out better ways to impliment these kinds of controls from within the pattern than me and guaranteed you guys know more about which effects do what to the OPL instruments than I do, the only one I know is the ZXX and I am grateful to have that at least.

Maybe this can be an idea pool for what pattern effects should do what... since there are a heck of a lot, and it would be useful to have (temporary) control over those sliders from within the patterns.

Either way I am simply brainstorming here and I hope the ideas are welcome. I feel like if we had more control over those sliders it would really help create variation in our tunes without having to make separate OPL instruments for each variation.