Code is safe, no backdoor or similar.
I check it
Thank you, Python is a fairly safe language to begin with, always good to be cautious though! The only security issue with this is the fact that your username and password are stored in plaintext, I plan to fix this soon by using console input to store encrypted versions of your original username, password, etc.
As you knew, I am not a fan of userscript, because I don't run any kind of business here, and simply would prefer to use given options/ features from forum. However, I have one suggestion for OP, that is: the userscript should allow users to set up their prefered timegaps between pumps, rather than a default (or only by now) with 24 hours per one bump (with delete of past bump, because it help users don't violate forum rules.).
This new option will help users to choose bumping their thread each three days or each 7 days.
Yea I will implement this in the next update, it's very simple to do. You could also do something similar by just changing the "interval" to a ridiculously high number, meaning the script would only check if a thread needed to be bumped every week, for example.