For example there are characters such as 熵 which as far as I know only means one thing - in this case entropy - and which have to have been deliberately added by some person or organization. An earlier example is the character 逛, which according to evidence in manuscripts of Dream of the Red Chamber was added to the language fairly recently, in the 18th century.
My question is: who / what at presently decides what new characters get added to the language? If we were to petition some one or thing to get the 招財進寶 rebus added to the language as an actual character, who would we petition? And do new characters added to the language have to have a pronunciation?