Kyan-
Was there a specific setting(s) you were looking to remove? Or were you
looking to set back to 'defaults' for some settings?
Generally speaking, settings would need to be removed via policy. In other
words, if you set a machine's security policy to LMCOMPATIBLITYLEVEL=2
(which is a GPO selection that puts a setting in the registry), then you
would need to process a lower setting in policy, such as
LMCOMPATIBLITYLEVEL=0, to remove that setting. It does depend on the
setting though since some are set in other places than the registry (such as
user rights), and some are defined in local policy, so removing a later
processing policy (such as from OU) may let local policy on a machine 'win'.