I have a number of questions about Intel PT (have been trying to decode the manual but is very difficult). My questions are:  

1. I am trying to find out if Intel PT can be disabled or reconfigured from within an OS, or, more generally, from within the system it is providing a trace of.
2. Does Intel PT generate events on writes to specific registers - such as CR3, IDTR, etc
3. Can Intel PT write values back to the system - i.e. can an external debugging machine actively perform writes to register, cache or memory?

Any help is much appreciated, thankyou!!