its incredibly hard to breed out hermy genes completely. Not worth trying.
The thing with hermying is that there are too low amount of hormones that regulate formation of female buds and they end up making some male buds easily. If the genes are good, small light leaks and stuff like that doesent cause the plant to hermie out easily. If a plant hermies easily from stress, it has poor genes, even if they would not hermie all the time or without inducing stress. The genes might be good enough for not to hermie in ideal conditions, but still its not good genes when it comes to sex.
The fact that some hermied tells that there is variation in these genes and if you keep breeding with them ,you will likely get hermies popping here and there, even if you try to outbreed them 10 generations, ofc rarer and rarer longer you breed IF ofc you select just the right plants for breeding. But how do you know if a plant carries genes that hermies easily, if they dont hermie in the perfect conditions? Well you dont. You could ofc try to stress the plants a bit and only choose the ones that dont hermie from a little stress, but it would be far easier to just start over.
If the seeds are just for personal use and you like the genes enough to grow them despite of hermie risk, go ahead, but i would not recommend growing them at all, let along breeding with them. But you do you, maybe you like playing with fire and will grow fire weed because of that
