Can I retain exiting transactions in an account but edit all fields for that account in the chart of accounts (for example, the name, type, subaccount charcteristics)?

A new business is new to Quickbooks as am I and it has entered transactions from inception into accounts that are largely defaults suggested by the software. I would like to revamp the chart of accounts to make it more suited to their business. This could involve changes to the account names, types, parent/subaccounts and implementing numeric codes. Is ths possible or are there fileds that cannot be amended. Also, can the business or an accountant delete unwanted codes or do they have to remain for audit log purposes? These may seem elentary questions but it does not seem sensible to test these things on live company data.