Andrea Melroe wrote a nice post over on the Dynamics GP community blog about this topic. Recently we faced the situation were we had to merge or rename numerous of your GL accounts in the various GP companies we have and it was affecting equally the different segments that were setup at the original system implementation. After the whole exercise, we went down from some 1800 GL accounts to less than 1200, that’s more than 30% reduction.
We used the two different approaches, depending on the amount of account that were to merge/rename : either the Excel / CSV import method, or the direct input of the segments to change. Both work equally fine and the decision to use on or the other only depends on the amount and type of changes you have to carry thru the system.
Remember to execute all those action while you’re alone in the system and with the ‘sa’ user only. Read the complete post here : https://community.dynamics.com/gp/b/dynamicsgp/archive/2013/01/22/is-it-possible-to-change-the-account-format-for-the-chart-of-accounts-in-gp.aspx