Great feature request!
I had the issue of trying out the “rules for ai” feature, which is basically a custom prompt, but it interfered many times, where it would output code (since that was the rule) when I just wanted text.
So basically one custom prompt limited me to use it for only one purpose, and changing or disabling the prompt was very tedious. At the end I therefore decided to not use it anymore.
An @Prompt feature with different pre-defined prompts for different purposes would be great!
Edit: Just found a comment for the same topic. How big is the impact of a custom prompt?
Most of the time gpt understands what I want, or I have to iterate once or twice.