By default, yui open will use default system text editor. But, you can specify any editor you like. I will use kate editor by KDE.

Navigate to application working folder

For Linux, default working folder is ~/.yui, for Windows, it is c:\Users\YOUR_USERNAME\AppData\Local\yui

Create config.yaml file with the following contents

---
editor: nohup kate % > /dev/null 2>&1 &
---

Save the file. Now if you try yui open it will open task using Kate editor:

How it works

kate %

This is console command, which will be executed to run edtitor, but % will be replaced by task filename.

Kate is feature-rich GUI text editor, so we run it in separate process

kate % &

But, this way editor is still linked to our console, we need to detach it, so it becomes

nohup kate % &

And we do not want any extra output from editor, so we redirect it to /dev/null
Final command:

nohup kate % > /dev/null 2>&1 &