Please review   Managing Custom Editors 

For example, try the following steps

Path = C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Microsoft SQL Server Tools 18

To explore how the editor choice appears in TimeXtender:

Right-click on a table > Advanced > Customize Code

Choose your editor

Note:  While you may view the SQL code in your favorite editor, I don’t recommend modifying the code.

Please study all TimeXtender training modules and Best Practices on Scripting, before attempting to modify anything.

Reference:  https://timextender.teachable.com/courses/1119367/lectures/23978916

(while the above link is for legacy training, similar concepts apply to the new release regarding Scripting)

@Syed Yousuf Is it possible to use it to edit custom views and store procedures?

No, those features already have a dedicated interface. 

Thank you for exploring the UI.