What do you mean by "silencing mods"?
The Plum doesn't need silencing for the upstroke since it comes with silencing rings pre-installed on the sliders. However, many of the keys could use some silencing on bottoming-out, but I don't know a good way to accomplish that. O-rings are not the answer, IMO, because that ruins the tactility of the switches and reduces key travel too much.
One thing I contemplated doing was putting some sorbothane acoustic dampening material in the case bottom to help absorb some of the bottoming out noise, but I don't know if that would have been as effective as I would have liked given that the keys which seem to be the loudest (and it is only certain keys, not all of them) sit over areas that can't accommodate the sorbothane material due to the daughterboard being in the way.
As for the rubber domes, you can swap them out for 45g or 55g domes instead, but that isn't something I'd want to bother with (but maybe you would). I bought the 45g version of the Plum Nano 75 just to avoid having to do a dome swap, and it is quite nice in terms of feel. The 45g domes are rigid enough to deliver some tactility, but still light enough not to induce finger fatigue.