Jessie, do you mean use non_UI tool such as pdm_load to create a new priority for requests but not incidents? If yes, I would like to point out:
--usually you don't need new priority...doing this could impact some out of box operations like priority caculation
--if you have to create a new priority, then you can just create it and then modify the detail_in.htmpl file change
<PDM_MACRO name=dtlDropdown hdr="Priority" attr=priority evt="onBlur=\\\"detailSyncEditForms(this)\\\"" lookup=no>
to
<PDM_MACRO name=dtlDropdown hdr="Priority" attr=priority evt="onBlur=\\\"detailSyncEditForms(this)\\\"" lookup=no whereclause="sym not like 'the-new-priority-sym%'">
so the incidents can't use this new priority.
Thanks
Chi