One may hijack one's own thread if the following apply:

One's new topic is mildly related to original topic.

One has asked permission from oneself to hijack one's thread.

If one hijack's one's thread, one must apologize, and if forgiven, may continue with new topic.

One has been given permission my administration because one acted irrationally about said hijacking.

And finally, if one states clearly to group that one is changing topic of one's own thread, it will not be considered hijacking, just one changing one's mind.