This item uses custom usrArray menu for weapon type choice.
it is not a tag-based choice - just harcoded array of possible values.
It looks like editor doesn't provide you way to modify it, so,
open your user file with any editor, find menu definition:
<arrayval field="usrArray" index="7" value="Short sword"/>
and add your Showel there:
<arrayval field="usrArray" index="8" value="Showel"/>
Don't forget to make Gizmo bootstrap conditional:
<bootstrap thing="wShovel">
<containerreq phase="First" priority="450">fieldval:usrIndex = 8</containerreq>
</bootstrap>