Hi EMB

There is no way to mass delete accounts, using Ledger itself. It's possible with Toolkit for Adagio, by Dakota Software. Toolkit lets you (among other things) merge two accounts together, which effectively deletes one of the them, and you can import mass merges from an Excel spreadsheet. The strategy is to create a dummy account called "Deleted accounts" and merge into it. But...

1) it costs money
2) you have to be careful because it doesn't check the balances
3) you can't only merge accounts with the same account type - Balance Sheet into Balance Sheet and Income/Expense into Income/Expense

One advantage of doing this is if you accidentally merge an account with a prior year balance, at least the trial balance will still balance.

Steve