What were you trying to do that didn't work?

When running wireshark, there is a certain sandboxing on the binary dumpcap in the system so that users can run the network traffic capture as regular users and not root. This is done by assigning the dumpcap binary ownership as 'root wireshark':

 # ls -la /usr/bin/dumpcap
 -rwxr-x---. 1 root wireshark 161544 Oct 13 02:00 /usr/bin/dumpcap

This requires a regular user to be part of wireshark group but on image-mode, the following command does not do anything and silently ends with return code 0:

 # usermod -aG wireshark testuser
 # echo $?
 0
 # groups testuser
 testuser : testuser

This results in a situation when the user tries to capture any traffic:

# su - testuser
$ tshark -i eth0
Capturing on 'eth0'
tshark: Couldn't run dumpcap in child process: Permission denied
Are you a member of the 'wireshark' group? Try running
'usermod -a -G wireshark _your_username_' as root.
0 packets captured

How does one add a user to a group in RHEL when using the image mode version of the system?