Yes, a conventional balanced diode mixer can swap the RF and IF ports. In fact, a diode DBM can swap (somehow) all the ports.
But your statement about this mixer: " ..its center frequency is controlled by a varactor (whose bias voltage is analogous to a mixers IF port).. ", makes me believe that this particular mixer can control through the IF port the mixer behavior.
What I do not understand (and here is not about swapping ports, which is just a lucky benefit of the diode DBM) is about that ONLY the IF port could change a parameter in the mixer, when this is not a valid statement in any other mixer type, where the IF port is only an output.
Anyway, I've seen many parametric mixers, but all of them use non-linear devices as diodes or transistors, or even non-linear capacitors.
I don't say this "filter type mixer" cannot work, but I was trying to understand it, and to find that was not invented just to appear in a triple E publication..