I meant snugging a nut up against the black thing to prevent the reso side rods from rotating at all. That would prevent the "lugs" from ending up at different heighths over time relative to each other and the hoops. A nut will turn freely on a bolt, but two nuts with a split washer in between tightened against each other won't budge. Any and all tuning would be done solely with the batter side rods while holding the black things so they don't turn. I understand that the design is still single-tension. Sorry if I wasn't clear before.
Also, you could "tune" the reso higher or lower by trying a 2 or 5 mil instead of a 3. Never tried it but it seems sound in theory. Alternately a thicker or thinner batter head would determine different relative tensions of the batter and reso.
I've messed around with old single-tension field drums and I was always able to tune them way better than I expected. I'm real finicky with my own snare, but I think with lots of head combo experimentation I could get "my" sound with a single-tension drum.