I don’t see why you would want to replace the ports with Variovents. If you don’t like the solution you’ve permanently modified your speakers.
You can approach this in a number of ways: Proac stuffed their ports with plastic straws. Dynaco used fiberglass sandwiched between steel mesh.
Firstly, the vented box will not give you lower bass. It will produce a higher bass peak, but actually roll off below the tuning frequency more quickly. A sealed enclosure will not have as high a peak but will roll off much more gradually, often balancing room gain. An aperiodic enclosure is a lossy sealed box, making the box seem larger to the driver since internal box pressure is reduced by leakage from the resistive port. On the return stroke, the port actually slightly resists the driver movement. If we stuff the port of the existing speakers, we are creating a hybrid between aperiodic and vented. This can be used to our advanced to tune the enclosure.
I would start by stuffing the port completely to se how it sounds sealed vs. vented. I would then remove the stuffing and slowly stuff a bit at a time until you like the tuning.
Another option is to cover the vent tube from inside the cabinet with a resistive fabric. A square of fleece is stretched over the sport tube and held in place with a rubber band. Listen to the result and add additional layers until you get the result you want.