press 'copy' in the filter editor; select the filter and press 'open'; then press 'paste'
then do the same with the second filter.
as it stands newspro just goes through filters in order and uses the first matching filter.
alternatively if you prefer to headers filtered out with the antispam filter to enter as deleted - you can just add the antispam filter in the kill filter pane in properties. in such a case there is no need to change anything in the watch pane and you can just select several newsgroups (kill filter pane) then press 'add' - the filter will be added to all newsgroups you selected at once.