Yes, there is. But it is a very small one, depending on the router model we're talking about and from which firmware is on it now and which firmware will be flashed to it, soon.
Most issues are not from a router update, but from Asus reserving 1MB of the JFFS partition for internal workings and this may break all scripts and other settings, including any VPNs that were configured previously. Or just a USB drive that coincidentally, 'dies' during the upgrade too.
When the move to 386.xx level firmware happens, a full reset to factory defaults will be the best way to get the maximum stability and performance the router can offer. This means a fresh install of the scripts too though.
No reason to worry. A fresh install of Diversion and other scripts is only a few moments of time to re-install from scratch.