How would I adjust this recipe to make it white chocolate? Would I need to melt/cool the white chocolate first or grate it and mix it in that way? Would I need to add/subtract anything (fat amount and sugar amount)?

My buttercream recipe:
1 stick butter
4 oz cream cheese
2 c. crisco
2 lbs powder sugar

Thank you so much.

Highly rated cream cheese/white chocolate American buttercream recipe:

http://allrecipes.com/Recipe/carrot-cupcakes-with-white-chocolate-cream-cheese-icing/detail.aspx

Here's a highly rated white chocolate American buttercream recipe:

http://www.food.com/recipe/white-chocolate-buttercream-frosting-130623

HTH