Why would you want to change dev fee address to your address when you're not the one who coded and developed the miner?
Given that you've build the rigs for your customers, wouldn't it be better if you just sell them at a profit? (which I think is what you're doing unless you're on to becoming a charity and/or a saint)
I am not changing dev fee, i want to set additional fee for me. The second fee.
There is a way you could do it - I'm thinking of it right now - but unless you are up-front about it to your customers this could be classed as theft (effectively installing a virus on there computer), and anyway they would soon find out and then the s**t would hit the fan.