I now know these controls inside and out. The answer to your problem is that Hynautic 'wick' the thread you are talking about when they assemble it.
Wicking solution is like a threadlock glue - you have probably noticed a green coloration on the ones you have managed to get apart. Wicking grade solution id designed to penetrate the thread and lock it preventing it from coming undone.
So, to get the thread apart, you heat it with a hot air gun to about 90 degrees (celcius - about 200F). The wick softens and the thread comes apart easily. There is no damage to inside parts