I would add another:
Which side is proposing a change?
The majority of PRIESTS went along with Vatican II, but that was going with the flow. Most men will always go with the flow. Also, when a CHANGE is proposed, there is a greater chance of that side being IN THE WRONG even if a majority ends up adopting it -- especially if that adoption is the path of least resistance ("going with the flow").
I might agree in general, but in a specific case I think you'd have to look at the character of the men involved and what we know about them already. Their fruits, personal sanctity, years of service, experience, judgment, moral strength etc. If they were all good and in order, I wouldn't presume they were necessarily being weak in this case. So there may be a difference in the two instances you are talking about (i.e. priests after Vatican II - many of whom were known liberals, some guilty of perversions or otherwise not suited for the priesthood, itching for novelty etc). Also, in some cases, it simply was a matter of faith, which some abandoned, set aside, or even preached against etc. I don't know that you'd say that that is the case here.
That being said, if there are sound and solid reasons on the basis of which a society like the SSPX takes a decision which, as you say involves some change, I think that same majority should lay out a clear statement of principles, and beside, consider it their foremost duty in justice to explain the reasons for the change calmly and cogently, most of all to their own faithful, who've supported them and invested much of their time, money, effort etc to their cause thus far who would understandably be disturbed.
And so far in my opinion these have not been forthcoming, for whatever reason, though I think more for unwillingness than inability, the Society's priests who have favored canonical regularization have hardly advanced publicly, for the benefit of their faithful - even those who might still agree with them - solid and convincing reasoning for the same. Obviously, as is only to be expected, if they don't, some Society faithful who see no reason for the cahnge, will suspect they are doing it for unworthy reasons and retract their support.