how to exclude package from repo

[Farkas Levente <lfarkas bppiac hu>]

hi,
is there any way to exclude package or assign priority to repository in
kickstart file? with yum one can exclude packages from a repo or with
yum-protect or yum-priority i can assign priority among repos (in conf
file). who can i do it in a kickstart file? eg. i'd like to install
kmod-xfs from centosplus repo during kickstart, but unfortunately
centosplus repo also contains a modified kernel while i wanna use the
base kernel. so with yum i can protect or give higher priority to base
and updates and in this case kernel not updated from centos plus, but
kmod-xfs can be used. of if i can exclude=kernel* from centosplus that's
another solution. but none of the above work with kickstart.
is there any way to solve my problem?
thanks in advance.

-- 
  Levente                               "Si vis pacem para bellum!"