Prefix/contextualize each conversation with a customizable message

Similar to customizable signatures used in e-mails, I would like to have a simple ui in ChatGPT with with I could have a customizable message that would be used as a prefix/context for each conversation. This way I could personalize my user experience, by p.ex introducing shortcuts or the like.

I can ofcourse copy/paste, but this seems like something that would be trivial to implement and could easily be provided by the platform.