See 2;4.2.3.2.5 of the ICAO TI:

"Classification of self-reactive substances not listed in Table 2-6 and assignment to a generic entry must be made by the appropriate authority of the State of Origin on the basis of a test report. Principles applying to the classification of such substances are provided in 2.4.2.3.3 of the UN Model Regulations. The applicable classification procedures, test methods and criteria, and an example of a suitable test report, are given in the current edition of the UN Manual of Tests and Criteria, Part II. The statement of approval must contain the classification and the relevant transport conditions."

This BAM No. represents the generic entry itself. The assignment to this generic entry is to be made by the competent authority.