The training method was actually pretty easy to find. If you just use some common sense, you will realize that a training method that doesn't use any "supernatural" power to train the body is easy to replace.
It's not perfect and still requires a bit of time and effort to change, but it is much easier than any of the others.
The other training methods use things like meridians, veins, aura, life force / vitality, spiritual images like tiger form, and even blaschko's lines.
Trying to change any of those would be a nightmare.
I did have a concern that if we ever managed to get a training method for energy or mental types that they might interfere with them.
Like using the meridians might interfere with future energy cultivation and that spiritual images would interfere with mental cultivation.
However, there is also the chance that they might boost or be beneficial to them instead.
