Long story short, I need to replace an electrical panel. In my the new panel the grounding bar is in a different location than the current panel. The ground wire from the Ufer rod will not reach to the new ground bar. Am I allowed to use a bonding terminal to "splice" a longer ground wire, or does it need to be one continuous wire?
There's an easier fix for this
Get a Siemens EC1GB82 ground bar kit and mount it to the bottom-most set of ground bar holes in your loadcenter cabinet, with the large lug down. Then, you can simply terminate the annoyingly short ground wire to the bottom bar's large lug and call it a day.
This works because all the ground bars on a panel are electrically equivalent -- the cabinet connects them all together, by virtue of itself needing to be grounded.