Best way to expand level 4 entries to more detailed level 5

[foxygramps]

When we switched our accounting system to Power Church, our bookkeeper set up most of the accounts as level 4 detail accounts. For example Utilities are level 4, detail account no 25-5030-000. This is the only account tracking utility expenses.
For the purpose of tracking more details of how we are spending our money, I want to change Utilities to level 4, Group, with the same account number. Then setup Electricity as a sub account 25-5030-100 as a level 5, group title. Then each of the Electric meter accounts would be level 6, detail, with account numbers 25-5030-110, -120, and -130. Water would be level 5, group, 25-5030-200, and the individual meters would be level 6, detail, 25-5030-210, -220 and -230.
Other accounts would be changed in a like fashion. This would only be on the copy I keep at home. We are just starting our accounting year.
What is the easiest way to accomplish this? I would like to retain the previos years data in its present form, with a thought of perhaps revising it later.