Question: Looping over entire worksheet

Is there a way to loop over an entire worksheet I already have? I am too lazy to retype everything into one for loop, and I couldn't just copy and paste everything into one command thing (the space you make when you shift-enter). Is there something I can put before my worksheet that runs it, changes one variable, runs it again, etc.?

Thanks! I hope it is clear what I am asking. 

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