Decades ago, there were no factory-made folding trainers. Those of us who trained in knife tactics carved, molded, or otherwise crafted non-folding trainers that had edges thick enough to make safe contact with a partner. Then, Eric Remmen started teaching his CLIP-IT self-defense classes, using "droned" Spyderco Delicas. The advantages of having a folding trainer that allows you to draw, open, and make contact with your training knife in one fluid continuum were huge, so Spyderco ultimately introduced dedicated Delica and Endura trainers.
Back in the day, saber grinds were the norm, so there was enough steel behind the edge to create a reasonably thick contact surface. Although not nearly as safe as the full-thickness "edge" of a dedicated trainer, they were OK. I have done this to knives like the Endura Emerson Opener for military students because that knife no longer has a dedicated trainer.
Full-flat-ground knives--like the Native 5--have thinner edge geometry. To achieve adequate thickness to train safely, you'd have to grind very high up on the blade. You'd change the profile of the blade substantially and reduce its weight to the point that it would not replicate the live blade well.
I would never allow one of my students or training partners to use a trainer with a thin contact edge. It may be OK on soft tissue, but if you actually train you'll quickly realize that the edge also impacts poorly padded, bony areas of the body and will break the skin. That's not speculation. I've seen it happen in training and have prohibited people from using makeshift trainers in my classes for that reason.
If you had to make a trainer out of a live blade, my current preferred method is to grind off the edge and point, then slit a piece of thin brass tubing (available at hobby shops) down its entire length with a Dremel cutoff wheel. Use JB Weld to attach the tubing to the edge to create a thick, safe contact area that still folds cleanly into the handle. I did this for Mike Seeklander, my co-host on The Best Defense TV show, for his Tenacious.
Curiously, I also "droned" a Tenacious as a prop for a scenario on The Best Defense. The host of the show, Michael Bane, was also the victim in the scenario. He raised his arm at the wrong time and--even with the blunted, polished, edge and rounded point--ended up donating blood.