First of all, that all depends on your definition of a positive result. I get a positive result almost every time I do hard drugs. Exceptions are bad dope, missing the vein, or getting arrested.
And yes, it is possible to do the drugs you have listed with minimal harm. It just takes a lot of extra effort.
Suppose you get a degree in chemistry (not that you necessarily need one for this). You could then cook your own meth, make your own PCP, make crack out of 100% pure cocaine, and make your own own heroin out of poppies you have grown. Once you have your substances, ingest them using the strictest precautions. If you take the meth and PCP orally, plug the heroin in your rectum, and smoke the crack once or twice, you will have escaped all harm (aside from a little lung damage which can be repaired). Neurotransmitters can be replenished with supplements like 5-HTP and L-Tyrosine. Vitamin injections, a perfect diet, and regular exercise will also help.
However, that doesn't sound very realistic, does it? It's very possible to use every drug you listed while still coming out "ok." With realisitc steps like a solid diet, regular exercise, vitamins and supplements, and getting the purest drugs possible, you can experiment with the hardest drugs and come out relatively unscathed.
In my experience, drugs don't change who you are. They may lower your inhibitions, making the craziest thoughts sound like a good idea. But those thoughts were already inside you.
With respect to addiction, I have found that it is mostly in one's head. If you think you need something, then you will act accordingly, and vice versa.
Again, if you educate yourself and take all the necessary precautions, it's POSSIBLE to do drugs with negligible damage. The real question is ARE you going to put in the extra effort. God knows I haven't.