You can pipe these mice two or three at a time, but they need to be decorated immediately for the decorations to really stick.
In the bowl of an electric mixer, sprinkle the gelatin over 2/3 cup cold water. Allow to soften, about 5 minutes.
In a small saucepan, combine remaining 1/2 cup water and the granulated sugar; stir over medium-high heat until dissolved. Stop stirring; clip candy thermometer to pan; wipe sides with a pastry brush dipped in water to prevent crystallization. Boil sugar until temperature reaches soft-ball stage (238 degrees). Remove syrup from heat; add to softened gelatin. Beat on low with whisk attachment to combine, about 1 minute. Increase speed to medium-high; beat until soft peaks form and mixture holds its shape, 8 to 10 minutes.
Transfer mixture to an 18-inch pastry bag fitted with a large, plain round tip. Mix sanding sugar with cocoa or powdered food coloring until desired shade is achieved. Spread in even layer in a rimmed baking sheet. Pipe a 2-inch-diameter mound directly onto colored sugar, pulling pastry bag to one side; the resulting peak will become the nose. Spoon colored sugar over top and sides of marshmallow until fully coated. Place pink decorette on tip to create nose. Place two dragees for eyes and two almond slices for ears. Insert licorice into marshmallow, creating tail.
Repeat step 3 until all the marshmallow is used. Store at room temperature in an airtight container lined with parchment paper for up to 2 weeks.