I opine that is not a minor modification in the effect it has on the innocent majority but requiring votes of the whole membership isn't justified imo, which I suppose makes it a minor change. I think the administrator should have a free hand, any objections should be aired on the appropriate board and changes made as the administrator sees fit.
It would be a shame if genuine signatures had to be sacrificed. I've just checked mine and I see I mention a community project. If it has to be ruled out, it has to be.
I have moderated a forum. All we moderators could do was delete or lock multiple posts (I favoured deleting). The administrator can ban IP addresses and, I would have thought, corporate slogans and certain words, both of which would be better than a blanket ban on signatures.
In short, I think it's a minor change but one I dislike.