Balance report

You can customize any of the Net Worth reports to only include a specific group of accounts, just hit the Edit button and go to the Accounts tab. And any of them can be customized to show increments by year or half-year using the Interval drop-down.

Your options are much more limited there. You can customize which accounts are displayed on the investing portfolio charts by command-clicking on the list in the accounts pulldown; I don't know any way to get something like that for non-investing accounts. Other than that, I think you'd have to export the report to a spreadsheet & make a chart there.