If you want to make a specific shield to add this skill, you have two options:
If you look at the _Shields entry, you'll see that under the column "Skills", it has "Shout_RecoverArmour". Since all shields are "Using" "_Shields", all shields should give the "Shields Up" skill.
What you can do is create a new custom entry "WPN_AnMaflinShield" based on "WPN_Shield" (or whatever other shield) and change just the entry "Skills" so it gives "Shout_RecoverArmour;Shout_ShedSkin".
After that, you'll use your new entry on the root template of the unique shield. Find the shield on the root templates and change the stats it's using to you custom stats.
You can also create a "_Boost_Shield_Skill_ShedSkin" and associate the boost to your unique shield.