Use CHANGING sparingly, where suited

CHANGING should be reserved for cases where an existing local variable that is already filled is updated in only some places:

METHODS update_references
  IMPORTING
    new_reference TYPE /bobf/conf_key
  CHANGING
    bo_nodes      TYPE root_nodes.

METHOD update_references.
  LOOP AT bo_nodes REFERENCE INTO DATA(bo_node).
    bo_node->reference = new_reference.
  ENDLOOP.
ENDMETHOD.

Do not force your callers to introduce unnecessary local variables only to supply your CHANGING parameter. Do not use CHANGING parameters to initially fill a previously empty variable.