I dabble in modding, myself. Content, mostly. My question is this:
I've added new, powerful items and abilities, looking at the existing items that are level restricted I found these lines
<Prereq>
<Type>UnitStat_Level</Type>
<Attribute>23</Attribute>
</Prereq>
Which I assumed would not let the character use the item until said level was attained. Lo, and behold, I saw the Umber Sov walking around with it at level 2... Thus, I either assumed the code was for what it isn't for or I did something wrong.
Then, when I added abilities I found these lines:
<Prereq>
<Attribute>UnitStat_Level</Attribute>
</Prereq>
Now, I set the rarity of the abilities very high (low number) so I haven't seen one in game yet to test if the level restrictions are working on them either. Do you think the second set of lines would work for items also?
Thanks, Evil.
*sidenote* I decided to attack the Umber Sov with that ring equipped, "The One Ring," with my ~ level 6, Sov + 3 champ stack of doom... Kul-Al_kulan wiped us out easily, 
