Once an Activity is created, it cannot be changed in the command-line Linux product. However, you can put the vtl command that you used to create the Activity in a script file and modify the script file as necessary. In addition, you can use a configuration file for the data collector's options by doing vtl activity -c -of (for more information, do vtl -help activity).
If you no longer remember the command-line used to create a particular Activity, you can examine the Activity by using vtl query -a . For instance, if there are three Activities in the project, and you want to examine the second one, do vtl query -a 2. vtl query -a without any arguments will examine the last Activity in the project.