It would be great if we could use the TriggerPRCommentBranchProperty and TriggerPRUpdateBranchProperty not only in Multibranch Items but also for branch jobs created via Organization Items.

It is currently not possible to set these property in a GitHub Organization job.
It is currently not possible to set these property via the properties step because it is a BranchProperty (see JENKINS-30519):

properties([
	[$class: 'com.adobe.jenkins.github_pr_comment_build.TriggerPRCommentBranchProperty', commentBody: 'rebuild']
])

The above snippet would fail with a ClassCastException.

Making it usable for Organization jobs would be a great improvement.