Hello ! About stems spliting you seems to have done great, take a look at that link and maybe it will inspire you if you want to continue in that way ๐ https://www.
instagram.com/savagedwc ๐. You can put your girl in the dark before harvest but 2 days is not enough to get the full potential of that method , 2 days will only delay your harvest from...2 days , if you really wanna do it then do it more than 3 days (4 at least) , but keep in mind that you need to keep the humidity low and a constant airflow to avoid any mold issue on your buds. Now concerning the purple colour you will have more chance to get it with a 16ยฐC to 18ยฐC temperature than by adding cold water in your soil , I don't know if it can induce the purple colour but it could shock your roots and slow your last flowering days , I would no recommend it but maybe I'm wrong. I hope it will help you ๐๐