Great that you've found a solution for your task!
It's unfortunate that some participants in this topic went into great lengths in understanding your requirements and suggesting possible solutions. What I can see from the conversation is a lengthy back and forth where you partly didn't pick up the suggestions or misunderstood what was suggested.
I kindly ask you to answer your last question by yourself. The forum here has a search function and Mp3tag has a help file where importing a text file via an action is discussed several times.
If you have trouble getting this running, please open a separate topic, explain what you've tried and what's not working. It's essential to invest a little time in explaining yourself and slow down to understand.