At first glimpse, your idea reads like you're blowing up a substitution cypher from "byte-level" to "word/sentence level". Also, I detect an initial but important security problem: you are weakening the crypto using your "blowup" strategy. 

Example: encoding *"attack at dawn"* using your crypto I would end up in 2 substitutions, while even a simple XOR-based crypto would mix up all 14 characters.

    MSG:    attack at dawn
    YOU:    green leaf          (where "green" means "attack" and "leaf" means "at dawn")
    XOR:    A_%2G6&§sxH%&d      

As you can see: in this case your crypto idea provides only 2/14 of the security compared to a simple XOR approach, which already gives ample indication that **it will be pretty easy to analyze and break**.

In the end, your idea is probably a good example to show why it's never a good idea to create your own crypto (that is, unless you know what you are doing).