Yes you can, there is a bo staff that is not craftable on horses_and_others.xml inside spitems folder, you can change many parameters in it such as; it's mesh and item usage. I tried making flag polearm beforer but I think it wont work now in newer versions.
<Item id="bo_staff" name="{=yy7RvQKN}Bo staff" is_merchandise="false" body_name="bo_spear_b" recalculate_body="true" mesh="axe_craft_32_handle" using_tableau="true" value="5" subtype="two_handed_wpn" weight="1" difficulty="0" appearance="1" Type="Polearm" item_holsters="polearm_back:polearm_back_2">
<ItemComponent>
<Weapon weapon_class="TwoHandedPolearm" weapon_balance="100" thrust_speed="100" speed_rating="100" physics_material="wood_weapon" weapon_length="100" position="0.0, 0.0, 0.3" swing_damage="5" thrust_damage="2" swing_damage_type="Blunt" thrust_damage_type="Blunt" item_usage="polearm_block_swing_thrust">
<WeaponFlags MeleeWeapon="true" PenaltyWithShield="true" NotUsableWithOneHand="true" TwoHandIdleOnMount="true" WideGrip="true" />
</Weapon>
</ItemComponent>
<Flags WoodenParry="true" DoNotScaleBodyAccordingToWeaponLength="true" />
</Item>
The problem with this is if you plan on making sword, and took the mesh from a blade, it wouldn't have a handle and vice versa.
Adding flag that CanBlockArrows will crash your game if you succeed blocking arrow with your custom sword. So just experiment until you are satisfied.