The question of practices other than faith comes up for Nichiren practitioners. Its complicated.
The Daimoku is an expression of this teaching - but its significant that Nichiren did not view the connection between the meaning (faith in universal Buddhahood) and the expression (the Daimoku) as absolute. He acknowledged that his 5 or 7 Character Daimoku was the same as Never Disparaging's 24 Character practice - something along the lines of "I would not dare denigrate you, you will be a Buddha!" The idea that meaning and expression are not exclusive comes back to the Lotus Sutra itself - particularly in the concept of Upaya. Zhiyi explores this relationship further, particularly in his FaHua Hsuan I - Profound Meaning of the Lotus Sutra - which is a thesis explaining that the entire Lotus Sutra is found in its title, the Daimoku.
For Nichiren, in this world, at this time, under the present circumstances, the Lotus Sutra is expressed in the Daimoku. The actual cause and effect conditions are critical, just as the transcendent, absolute aspect of the Daimoku is equally critical - and when understood correctly, are the same Truth. (Notice the Threefold Inclusive Truth structure here.)
Nichiren also wrote about "reading with the body". The Lotus Sutra is not something to merely be chanted, but it is something that is meant to be lived. Nichiren viewed his life as the text of the Lotus Sutra itself. In this sense, all activities, when undertaken in the spirit of faith, become the reality of the Lotus Sutra. This would mean that anything we do is practice. Chanting the sutra is the Lotus Sutra. Shodaigyo is the Lotus Sutra. Breath counting meditation is the Lotus Sutra. Observations of the 18 sense fields is the Lotus Sutra. Threefold contemplation of reality is the Lotus Sutra. Going to Yoga class is the Lotus Sutra. Going to school, work, a football game is the Lotus Sutra. Shopping for a pair of prize shoes is the Lotus Sutra. Benching 350 lbs is the Lotus Sutra. Certainly, telling another even a single phrase of Buddhadharma is the Lotus Sutra. It goes without saying that insisting on interacting with all beings as though they were full blown Buddhas is the Lotus Sutra.
This might sound like a simplistic and naive practice - but anyone who has tried to undertake this practice, in its simplicity, will confirm the extreme difficulty. In practical effect, in order to really live this practice, I think, you actually do have to undertake a variety of practices like breathing meditation, contemplation of the foulness of the body, contemplation of the senses as senses, the conventionality and emptiness of dharmas, the compassionate vows of the Bodhisattvas, etc. etc. The distinction is that where some schools take one or another or even a series or groups of these practices as a primary practice that is believed to result in annuttara samyak sambodhi, Nichiren denies this; unless framed within the Buddha's own view and practice - a firm belief and understanding for the highest regard for your own life as well as the life of all other beings - the real meaning of the Universality of Buddhahood according to Nichiren - these practices are dead ends - ascetic practices divorced from the ultimate goal.
My sense is that Nichiren proscribed practices other than the Daimoku for the same reason exemplified in the Milk as Medicine parable from the Mahaparinirvana Sutra. There was too much confusion concerning these other practices so rather than try to explain their proper application within a Lotus Sutra context, he just proscribed them in favor of the single precept of faith. I don't think that proscription is meant to be permanent, but then, I could not venture to suggest that the time is appropriate for that proscription to be set aside. I think we all have to make decisions about how we live our lives for ourselves. No one can tell us. We have to be lights for ourselves.