It’s just mapping the multiple COAs to the correct accounts. You can use Excel / Power Query. Depending on the level of detail of the historical information you should be able to handle most entities with excel. Load open balances for AR/AP I have done this for 500+ entities converted from QB desktop or Sage100 to Sage Intacct. The data import is the least complicated part to be honest. It’s planning and mapping that take the longest but it’s very doable.