So you need to resize some VM images, and possibly inspect them later. Here's the dope:

 mount_loopback.sh
# Replace size with what you see to be appropriate
qemu-img resize $IMAGE_FILE +80GB
# Setup a device for the image file so that we can resize the relevant partition
losetup -f -P $IMAGE_FILE

When using LVM, you'll have to do some extra steps to get the relevant device and resize things:

 get_mapped_volname.sh
pvscan --cache
# Grab the name of the volume
lvs
# Use the name from that to plug it in, there should be something similarly named in /dev/mapper
vgchange -ay

Now you need to resize the partition:

 resize_normal.sh
# When you have a normal DOS/BSD partition table:

# Using ext fS:
resize2fs /dev/loop0p1

# Basically anything else
growpart /dev/loop0 1

Things are of course different on LVM:

 lvm_extend.sh
# Resize partition you want, usually this is device 1, but on XFS the data section is usually device 2
pvresize /dev/loop0p2
lvextend -l +100%FREE /dev/mapper/$NAME

XFS also requires special handling. You will have to mount the relevant device and then:

 xfs_grow.sh
# Or, the loop device if it's not LVM
xfs_growfs /dev/mapper/$NAME

Mounting and fiddling with stuff is as simple as:

 mount_loopbacks.sh
# Replace partition number with whatever is appropriate
mount -t $FSTYPE /dev/loop0p1 $MOUNTPOINT
# Same story with LVM stuff, but use the /dev/mapper entry
mount -t $FSTYPE /dev/mapper/$NAME $MOUNTPOINT

When done, you should remove the loopback device:

 remove_loopbacks.sh
losetup -d /dev/loop0

One last point worth noting is that if you do this while the VM is active writes will not show up until you unmount & unload the loopback devices, as they don't share journals. The best use of mounted VM disks on the hypervisor is for backups though, and for this purpose loading and mounting them just for the backup period works quite well. As such I generally also add the -r (read only) option to losetup when I'm mounting for backup purposes.