Spiritual pursuits have an incredible creative aspect. People can set up their spiritual practices on any scale they wish. Anything goes. The catch is that the creation takes on an internal logic matching the scope of of the spiritual practice. Compliance to a driving internal logic molds people's actions on so many levels. The logic of a spiritual practice can estrange it from other definitions. The challenge to the cross-group dynamics is that one spiritual practice's internal logic will not be congruent to another's. In fact, it takes a lot of effort to get groups to match. One of the reasons traditions are created is so there will be some congruency of internal logic. This reason by be subconscious, but it is there nonetheless. The most hardened traditions attempt to lock in a set of rules, but these fixed precepts originally came from some creative source. It is terribly practical and human that spiritual practices are seen to be a creative pursuit.
Spiritual practices can and will change. The changes may be very difficult or the changes may be very easy. The relative ease is determined by the existing internal logic and the desired state of the change. the 'explanation' of the change must fit into the existing internal logic of the spiritual practice. A person must be even more creative than the originator of the spiritual practice when a change is especially contrary to existing logic. Especially contrary changes or additions are disapproved by those who cannot explain the extension of the logic. Complete investment in a spiritual practice can put a person in a place where it is difficult to accept or promote any change. Agents of change often must then come from the 'outside'. This outside can be truly on the exterior of the spiritual practice or it can be an internal force that sees looseness in the internal structure. The agents of change provoke changes in internal logic that the vested insiders cannot.
In the end the spiritual practice becomes a helpful tool, too limiting to realize the full scope of the divine or connect all interpretations of the divine together, but it is enough to state, "this is what I believe in all its wonderful and insightful wackiness".