Yes you can hybridize but that means you need to cross pollinate then isolate the plants you've cross pollinated so they don't get contaminated. It's a painstaking process and will take years of trial and error. I'm sure if you go to library you can find books on the subject.
Healthy growing won't genetically change the seed, that comes with sexual reproduction......the pollination. However, by selecting only the best plants to save seed year after year you are actually doing some genetic manipulation by "survival of the fittest." In fact going with really healthy soil may not give you those tough seeds you are looking for. Pamper them to accept only perfect soil, eliminates those that can tolerate adversity and still perform well. Start your experiments with nonhybrid seeds. They may be called heirloom or open pollinated. Hybrid seed does not produce new seed like the parents since they themselves are from mixed heritage. They will cross with each other and may produce plants that reflect a parent (which may not have all the desirable features) or something really weird. But through selection for season after season even these can be selected for a somewhat stable variety. I agree, study up on genetics.....it is fascinating.
