On the other side of the planet we get a lot of what I call non-exclusionary religions. Hinduism is one example of that because they believe all religions are part of Hinduism. But on a less escoteric level Shintoism (ancestor worship) and Bhudhism (which is really more of a philosophy but people call it a religion) have no rules against following other religions as well. Technically one could be a Hindu-Shinto-Bhudhist and not violate any rules of any of the religions. Strictly speaking (and I'll probably get called a blasphemer for this but I'll say it anyway) since Bhudhism doesn't involve any form of worship but is rather focused on self awareness and analysis (Bhudha is respected as the person who figured out the path to enlightenment but, at least in most sects of Bhudhism, he's not worshipped) you could be a Christian-Bhudhist and not break any of the rules (because no part of Bhudhism involves worship a god other than God and there's no idol worship). Arguably the Benedictine Monks follow a very Bhudhistic path within Christianity (they even dress very similarly to Bhudhist monks) but where Bhudhists meditate Benedictines pray.
I would get into the logical fallacies I think are plain as day in Christianity, but it's early, I'm not all the way awake and I don't think I could do so without getting rude, something I am trying hard not to do.