For those with flatter home network needs but still wanting a few things internal to be reachable by IP I'll throw in you can also use static link locals on fe80:: instead of a random ULA prefix. You'll still need the ULA method if you have multiple subnets and want static services reachable via routing though.
Unless the router says the old prefix now has a valid lifetime of 0 the proper thing to do is actually to wait for the prefix to expire like it seems to be doing. I never had this missing lifetime change problem with Comcast but it's very possible they do things differently in different service areas/for different service types.
Link local addresses work the same as IPv6 addresses in the url bar, just make sure you're entering the full link local and not the first portion only. Static IPv6 is horrible to enter in browsers in general because you have to remember to [address] as well. Of course, if you're doing it for statically configured local DNS entries as in above then all of this is moot as you'd just use the name.
Unless the router says the old prefix now has a valid lifetime of 0 the proper thing to do is actually to wait for the prefix to expire like it seems to be doing. I never had this missing lifetime change problem with Comcast but it's very possible they do things differently in different service areas/for different service types.