First stage dealer - excise duty

Hi!  Our company is dealing with sales of several products.  For a major product, our customer is asking us to get registered for excise so that we can pass the excise duty. My question is;

1.  If we register as first stage dealer, should by default we include Excise Duty for all products we sell?  All our other products cannot be sold with ED. Please clarify.

2. If we do Even billing, our customer will know our Profit Margin which we dont want to reveal.  What is the way out to pass ED to our customer without them knowing our profit margins?

Please assist.

Thanks and regards

Santhosh