Pulling the whole;
Omens in thickets are fortunate.
Hau Young Owl Hatching,
It would not be proper for anyone to alter the sacred ceremonies for their own purpose. These ceremonies were given to the People from Tunkasila, and they were instructed on how to properly conduct them. These instructions are very important and include such things as the preparations, the songs, and the gestures that occur within the different ceremonies. If any of these instructions are overlooked, or modified, a particular ceremony most likely will not have the impact that Tunkasila intended it to have. Granted, many leaders may make slight modifications to portions of certain ceremonies either due to personal visions or out of necessity, but the bulk and heart of the ceremonies remain unchanged.
If your non-Indian friends have an honest affinity for native ceremonies, they will understand this, and will not try to change or modify any of our sacred ceremonies into their own "superficial rituals". If their affinity is truly sincere, they will find natives who will invite them in to observe or participate in certain ceremonies, and Tunkasila will ask them to do so.
For what it is worth, I have prayed once in a non-Indian, New Age sweat. I went there because I was told it was run "Lakota style." These people did things before, during, and after the sweat that were not Lakota, in fact, these things were not even Indian. But I went there to pray with a good heart, and not to criticize, so I said nothing. As far as the physical act of sweating went, I did sweat there. But spiritually, their lodge did little for me; the Spirits were absent and I left with an empty feeling.
This example is given not to rip on the New Age people, but to make the point that the instructions given with the seven sacred ceremonies were done so for a reason. To change and modify these instructions, along with incorporating these ceremonies into your own personalized rituals, diminishes the spiritual power and purposes that Tunkasila intended for them, and these things, therefore, should not be done.