Thank you very much for your comment.
As you well mentioned, you are not currently able modify the content of an activity, but you can add or edit any information you wish the students to see in the 'Student instructions' field.
As shown below, this information will be clearly visible to the students when the activity starts.
I hope this helps and rest assured that your suggestion is something that we are aware of and that will be taken into consideration in future updates.
Have fun teaching!
The EF Class Team