Attunements are one of the areas that Open Source Reiki practitioners have experimented with. Not every practitioner senses energy in the same way, and thus the same attunement method may not be appropriate for every practitioner.

It is strongly held theory in most Traditional Reiki practices that there is only one correct formula for attunements, and alteration of the attunement process will ruin the attunement. At the same time, Diane Stein in Essential Reiki points out that from the moment you are attuned for Level I (Usui) Reiki, you have Reiki Guides who will "fill in for you" when you make a mistake passing attunements.

In conversations with my Reiki Guides, most significantly Bob and Lee, I have been told that the normal dogma about specific formulas for passing attunements is misguided. Visual practitioners can draw symbols in the air, somatic practitioners can choose to do so as well, but vocal/audial practitioners can chant, etc. The basic attunement principles are the underlying whys not the hows. Lee tells me that they would also attune in groups, either by doing a round-robin for the attunement process or several practitioners on a single student at the same time, with certain teacher-masters attuning a subset of symbols rather than every person having the burden of remembering all the symbols to pass. In other words, the thought of a single practitioner remembering 500 reiki symbols, and taking the time to pass them all in a single-teacher attunement, was ridiculous.
--The Crisses

It becomes obvious that the Usui method of passing attunements, especially Level 3 attunements, would be ridiculous for a repertoire of 500 symbols. Open Source Reiki practitioners have experimented with several methods of passing attunements.