I have to replace the router and I’m wondering if the new WiFi password has to be initialized on each connected device? It looks like a huge job, as if the whole system is being built from scratch.
Unfortunately, for most devices this will be a necessary action. Only some newer Sonoff devices allow you to change the password in the eWeLink App. This, of course, requires a parallel WiFi network - old and new. Both networks must have different names (SSID).
There is, however, a simpler solution. Let the network on the new router have the same name and password as the network on the old router. Save the settings and switch off the old router. Switch on the new one, connect it to your computer with a LAN cable, change the default (factory) WiFi settings. Done. Or at least it should be done 