These examples show what hopefully will be possible with augeas one day.
For now, they are more a guide in writing the public API and augtool.

1) Change default runlevel

  p = match("/system/config/inittab/*/action", "initdefault")
  set( join(dirname(p), "runlevels"), "3")

  [works]

2) yum

  - enable a repo
    set("/system/config/yum/myrepo/enabled", "1")

  - turn off mirrorlist and set baseurl
    rm("/system/config/yum/myrepo/mirrorlist")
    set("/system/config/yum/myrepo/baseurl", "http://yum.example.com/repo")

  [not implemented, needs ini scanner]

3) add entry to hosts
   set("/system/config/hosts/i0/ipaddr", "192.168.1.1")
   set("/system/config/hosts/i0/canonical", "pigiron.example.com")
   set("/system/config/hosts/i0/aliases", "pigiron pigiron.example")

   [works]

4) add to fstab [tree structure will probably look different]
   p = "/system/config/fstab"
   rm (p + "/dev.vg00.local/local")
   set (p + "/dev.vg00.local/local/device", "/dev/vg00/local")
   set (p + "/dev.vg00.local/local/mountpoint", "/local")
   set (p + "/dev.vg00.local/local/fs", "ext3")
   set (p + "/dev.vg00.local/local/options", "defaults")
   set (p + "/dev.vg00.local/local/freq", "1")
   set (p + "/dev.vg00.local/local/pass", "2")

   [requires fstab provider, easy, based on record scanner]

5) Mount /dev/sda1 on /exports/foo rather than /foo
   p = "/system/config/fstab"
   move entries from p + "/dev.sda1/foo" to p + "/dev.sda1/exports.foo"
   set(p + "/dev.sda1/exports.foo/mountpoint", "/foo")

   [same as above]

6) Change gateway on all static interfaces
   for p in find("/system/config/sysconfig/interfaces/**/gateway", "192.168.0.1")
     set(p, "192.168.0.254")

   [requires key/value scanner]

7) Setup a static interface from scratch
   p = "/system/config/sysconfig/interfaces/lo"
   rm (p)
   set (p + "/device", "lo")
   set (p + "/ipaddr", "127.0.0.1")
   ...

   [requires key/value scanner]

8) Turn on SELinux
   set ("/system/config/sysconfig/selinux", "enforcing")

   [requires key/value scanner]