If your shell script is simply a sequence of configuration commands (such as uci set, uci commit, etc.), there’s no need to create a 3-task group. You can paste the script directly into the command text box and execute it as a single task.
My shell script is indeed more complicated. It contains conditions, reads and writes files from the file system and so on. I think what you say confirms my understanding that the command text box does not support such complex cases.
Thank you for the info about executing tasks. I wasnt aware of that feature.