Hello JaneS,
Changing the account structure is actually not an issue from a technical AX perspective.
You should try closing all pending transactions such as open but not posted journals. Otherwise users will get an error message saying that they have to enter all journal lines again because of the account structure change.
Other than that I would recommend that you activate the new structure at the end or beginning of a business day when not many users are working in AX.
If you are not absolutely sure what and how to do the change ... make a test run in a demo environment first.
All the best,
Ludwig