How do I start a business in my country when there is company already using the same idea in business in another country?

I have a couple of issues I need to address before I can start my business idea. The first issue, is that my idea consists of making alterations to a product that a large company makes and distributes to retailers for re-sell. Am I able to buy wholesale amounts of this product, just as a retailer would, and make the alterations to this product as I please? Or would I need to seek permission from the company to be able to make these alterations before I sell to consumers? Would I need to pay royalties? If so, how do I go about seeking permission? My other issue, is that this idea has already been put to practice by a company in the US (I am in Australia), but they have a very minute market in Australia due to the overly large shipping and customs fees. They have a pending patent according to their website. Does this mean I will not be able to set up a business with the same idea? Is there any way for me to go about legally starting up a business with this idea?