How to modify a payload?

[Jordan Trover <shurimaxx () hotmail com>]

I am trying to modify the download_exec payload from metasploit, I basically just need to execute the downloaded file 
with an argument, I read the file /modules/payloads/singles/windows/download_exec.rb but the payload is already encoded 
there.
So what the best option here?, should I create my own payload with the language I feel confortable (c++), or is there a 
way I could modify the existing to execute the downloaded file with an argument?

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