In a small mixing bowl, combine sweetened condensed milk with 1/2 cup key lime juice and stir with a whisk. You can also add a tsp of fresh lime zest to this mixture.
Place mixture inside a piping bag with a Wilton #230 filling tip attached.
While holding a cupcake in one hand, use other hand to insert a cupcake filling tip in the middle of the cupcake. Slowly pull tip up and out as you feel the cupcake start to expand with filling. Repeat procedure with all 24 cupcakes.
Prepare Frosting:Using an electric mixer, whip butter in a mixing bowl until fluffy. Add sugar, salt, lime juice and vanilla. Blend slowly until incorporated and then gradually increase speed until frosting is smooth and creamy.
Separate 1/3 of the buttercream frosting into a bowl and add orange food color gel to it. Blend until uniform and place into a decorating bag with a star tip attached. Set aside.
Cupcake Assembly:Use the remaining white frosting to spread a thin "crumb" layer of frosting onto the top of each cupcake and then refrigerate for an hour or so to allow it to firm up.
After crumb layer has set, fully frost tops of cupcakes using a flat frosting spatula to achieve a smooth surface.
Place a hat on top of each cupcake and then add the candy eyes and one chocolate sprinkle for each eyebrow. Add a jellybean nose and then pipe orange frosting to create a beard onto each cupcake.