Not a major change, just the addition of some connection points…
Put in a row of breakout pins (eg: J2 as per J1) - probably need to reloate C17 & R1 to put it in the corner or otherwise put it in the space near C5 & C9
First priority, put ADC6 which is currently not available at all.
Second priority, put PD2 & PD3 so they can be monitored.
Finally, put PB2, PB3, PB4 & PB5 so they can be monitored.