What were you trying to do that didn't work?
If I use two options simultaneously, I still can execute ‘systemctl restart qemu-guest-agent’ with no error output, but sometimes failed, and there is no obvious error content about warning users don’t using them at the same time, is that friendly?

Please provide the package NVR for which bug is seen:
qemu-guest-agent-8.1.0-1.el9.x86_64

How reproducible:
100%

Steps to reproduce
1. start VM with qemu-guest-agent-8.1.0-1.el9.x86_64
2. change files '/usr/lib/systemd/system/qemu-guest-agent.service'&'/etc/sysconfig/qemu-ga' 
3. restart qemu-guest-agent.service  

Expected results
restart/start failed with obvious warning/error output

Actual results
[root@newhostname ~]# systemctl restart qemu-guest-agent.service 
[root@newhostname ~]# echo $?
0
[root@newhostname ~]# systemctl restart qemu-guest-agent.service 
Job for qemu-guest-agent.service failed because the control process exited with error code.
See "systemctl status qemu-guest-agent.service" and "journalctl -xeu qemu-guest-agent.service" for details.
[root@newhostname ~]# systemctl restart qemu-guest-agent.service