Snowgolems on their own are't very useful.
Exept snowfarms, and baiting hostile mobs into traps, there aren't many practical uses for them, and their combat usefulness is close to zero. So...what if upgrading snowgolems with ice blocks would be possible? Then, with permanently increased armor and damage they could somehow help you in fight. The value of armor and damage of the "iceballs" increased with left-clicking with an ice block on a snowgolem should depend on the type of ice used.
+3 armor points
+1 damage point per "iceball"
+5 armor points
+2 damage points per "iceball"
+10 armor points
+3 damage points per ice ball
And grants immunity to rain damage
But all of that could be changed for the sake of ballance. And also, upgrading a already upgraded snowgolem shouldn't be possible. Just to not make getting a snowgolem with ridiculously high amount of armor and damage.
And another thing, every single "level" of a snowgolem should have it's own texture, just to be able to tell what statistics the snowgolem has. Same with "iceballs" to tell how much damage they deal.