Siping is a leftover from the days of bias poly tires when snow tires had large rubber blocks and tire technology predated the ability to mold in the additional slots. Unslotted large rubber blocks are terrible on ice.
Today's tires are highly engineered in their design and the additional slots, which add edges and allow some additional tread block distortion to "bite" the ice, are designed into the tread on winter tires. In addition, modern tire carcasses flex more than the old bias ply tires, to allow the tread to lay flat on the road surface. That changes the whole effect of siping.
Siping tires not designed for the additional slots can result in additional heat buildup as well as reduced mileage due to the additional tread distortion that siping allows as well as reduced tire life. The heat buildup can result in premature tire failure.
I strongly recommend against siping in modern tires. If you want/need good winter traction, buy winter tires.