While the Leaden Plating feature is simple one of its feature can not be applied to a Shillelagh weapon. I have an alternate idea.

Transmutation
At 1st level, once after a short or long rest you gain the ability to transmute the shape of a weapon or change the properties of armor, object or construct. You regain the use of this feature after you complete a short or long rest.
•Weapon; you touch one melee weapon, 20 pieces of ammunition, or up to 5 darts. Doing so allows you to change the damage type of the weapon to either bludgeoning, piercing, or slashing damage. This effect lasts for one minute.
•Armor Resistance; you touch one suit of armor, one object no bigger than a 5ft cube, or one construct giving it resistance to either bludgeoning, piercing, or slashing damage. This effect last for one minute.
•Vulnerability; you touch one suit of armor, one object no bigger than a 5ft cube, or one construct giving it vulnerability to either bludgeoning, piercing, or slashing damage. The target of this feature must make a charisma saving through to be affected. This effect last for one minute and requires concentration.
That is my idea, I’m sure you could word it better.