The steps, especially steps four through nine, seek to rewire one's whole approach to life.
It's usually not wise to adopt another programme seeking to achieve the same purpose at the same time, whether another twelve-step programme, or another spiritual, psychological, or religious approach.
Maybe the other approach needs to be adopted first, with the steps coming second. Who knows? But riding two horses is very hard. There can be conflicts. Attention and energy is split, and this slows both processes. And it's impossible to see which is helping, and how.
Over the last 28-plus years, I've done a number of things, including the steps, more than once, plus other spiritual, psychological, and religious programmes. All have helped. But I've done one at a time. When I tried to do more than one at a time, all hell broke loose. However, individual, targeted measures can certainly and usefully be adopted as bolt-ons, particularly where they provide instant, symptomatic relief. Any approach seeking to rewire one's whole approach to life is necessarily going to be a long process and will not therefore provide much if any relief. In fact, it will probably add greater challenges and so be inappropriate as a response to an acute condition.
If a person is part-way through the steps but is experiencing emotional challenges, the answer is usually to find quick, simple fixes to improve the day, not to embark on a second long-term holistic solution. In other words, maybe get a mindfulness app and meditate simply for half an hour a day, rather than undertaking a systematic course in Buddhism, which will actually deepen the distress for a while before it helps, because it will challenge core beliefs. I know. I tried!
Obviously, each case must be judged individually, but these principles will usually hold good for most people.