I can't speak to your question regarding chronic versus complex PTSD. As for stopping unwanted thoughts... I have to say that I don't believe there is any way to stop unwanted thoughts from popping up. And I've never read, or heard, of anything either. In fact, everything I've read suggests that trying to do so is the surest way of making certain they'll keep coming.

There is a practice that is referred to as compassionate abiding, whereby one allows thoughts to arise, accepts them, & then allows them to fade at their own pace. Here's a link to a mental-health-oriented description of the practice:

https://mindsetdoc.wordpress.com/201...e-abiding-101/

The other thing I sometimes do though, in an effort to cease ruminating on particular thoughts, is to chant mantras. If you're not familiar with mantras, there are lots of them from various spiritual disciplines on YouTube.

I wish you well...