Thanks for asking Momu, and as promised here’s my reply. Adding to all the answers from Amarantians, I searched for the topic on theme and found this article Stage 8 - Setting a concise Theme for the session
Adding to this you can also read the book “Why me” where I also talk about the non-linearity of cause and effect 
Bottom line… theme finalisation is a prerequisite to start the PLRT process and it can change (read as evolve) as long as it’s the direction of going deeper to the cause, getting refined and distilled.
