Stiff Consistency: In large bowl, combine 2/3 cup water and meringue powder; whip with electric mixer at high speed until peaks form.
Add 4 cups sugar, one cup at a time, beating at low speed after each addition.
Add remaining 8 cups sugar and 3 tablespoons water, shortening and corn syrup in 3 additions, blending well after each.
Add salt and flavorings; beat at low speed until smooth.
Keep bowl covered with a damp cloth until ready to use. For best results, keep icing bowl in refrigerator when not in use. Refrigerated in an airtight container, this icing can be stored 2 weeks. Rewhip before using.
For thin (spreading) consistency icing, add up to 4 more tablespoons each water and corn syrup.