This makes me wonder: How hard would it be for companies to offer slightly customized funds? For example if I wanted to invest in S&P500 minus XOM. I might need

This makes me wonder: How hard would it be for companies to offer slightly customized funds? For example if I wanted to invest in S&P500 minus XOM. I might need to pay higher fees, but it's probably doable. (The reason I want that is partly boycotting environmentally unfriendly companies, partly a belief that they will not grow anymore, for the reasons mentioned in the article.)