The key to rapid culture change in any organization is process, not people. First focus on changing processes. Attention to people comes later.
For example, in working with a leadership that was having difficulty in coming to consensus and making decisions in a timely manner, I asked them to try a process I had developed. Unconvinced, they humored me and gave it a try. As a result, they worked through a list of seventeen strategic issues requiring decisions in two hours. Previous efforts had taken weeks with no result. The CEO and many of the managers had ascribed cause to cultural and communication issues, or otherwise to personalities of certain individuals in the group. Yet simply changing processes fixed most issues right away.