It is generally done by end users. Anything extremely technical can be done by Alacrity Inc. staff or IT staff. As a general rule, ARM is an order of magnitude less maintenance intensive than an information warehouse or relational database application. ARM is not likely to cause any problems. You can dynamically add new pieces to your business.
End users can set up conversion tables between different charts of accounts.
In fact, ARM is design to support different planning, budgeting, modeling and performance reporting for different areas of the organization. ARM can be easily changed. And if different senior managers want different views of the organization, we can support multiple views of the organization. My organization is very unsophisticated. ARM is designed to permit gradual evolution of the system.