This is one of those simple “rules” that have no exceptions in the tradition of mainstream church organ playing. The idea of using the tremulant in large organ stop combinations has its origin in the theater organ world. While appropriate in that environment, it is not appropriate in traditional congregational hymn accompaniment for at least two reasons:
If you have used the tremulant in this way before, and find it difficult to go without it, just try it for a while. Shift your focus on assertively and artistically leading the congregation, and you should find hymn playing without the tremulant to be very satisfying and uplifting.