How to update stdout coming from internal command?

I’ve a bash script which uses internal script and internal script is interactive in nature.

Sample Output :

Speed: 1MB/S File_in_process: xyz.tar
Files extracted: file1, file2... fileN
...
...
Task completed successfully. 
# wrapper script operation
headers updated of file(1-N)
Script completed successfully. 

I need help in either to remove Task completed successfully. or update with ABC Task completed successfully, because it is very misleading and getting two success messages. I’m trying with /dev/null and awk but no luck in changing only a single line. Please share some ideas.