guestfish

I'm trying to figure out the proper way to use guestfish in host down scenario. Say, we have a RHEV VM that won't boot and the possible fix is to modify a config file (i.e. lvm.conf). How do I go about using guetfish to mount that file system so I can make a change to the configuration files? Basically, I want to know how to use guestfish in RHEV similar to using a rescue disk.

In the past, I tried by activating the VM's logical volume, then mounting it with guestfish. Doing this actually caused more issues that I was never able to resolve. Unfortunately, it was long enough ago, that I don't remember the exact issues.
Thank you,