My new bees may have already affected the feral hives by breeding with them.
What you are hoping for is the opposite. You want your production bees to gain the survivability of the feral bees without picking up the aggressiveness. Your interference becomes simply eliminating the colonies (or just the queen) that don't meet your criteria and letting the ones die that can't make it on their own. As a back yard beek you can afford to do this. However it would be a poor business model for a sustainable income. I maintain only three hives. Most of the ones that died on me were because I did something stupid. So if you can read about all the stupid mistakes that people make with their bees and not do it yourself you are further ahead. It is harder then you think. I have been pretty creative on coming up with new mistakes.
Some people try to use just feral bees. But these bees are not very productive and they swarm a lot. I think you are better off taking the advantage of many years of professional breeding until you find one that can make it through it first year and then splitting to gain the feral genetics in your area.
Many people claim they get good production from feral bees and cut outs but how do they know that the bees are actually feral and not just a swarm from a managed hive? The one thing you have control of as a beekeeper is the hive (structure). You can replace comb and move it around. A feral bee has to leave (abandon) the hive so another insect can come in to clean it out. Once cleaned out another swarm can come in and make new. That is the only way a feral bee can rotate out old comb. Keep in mind that most feral hives are small in comparison to a managed hive.