How do I change a project's id in SBT 1.0?

I have a bunch of SBT 0.13 project definitions that look like this:

lazy val coreBase = crossProject.crossType(CrossType.Pure).in(file("core"))
  .settings(...)
  .jvmConfigure(_.copy(id = "core"))
  .jsConfigure(_.copy(id = "coreJS"))

lazy val core = coreBase.jvm
lazy val coreJS = coreBase.js

(Mostly because I'm resentful about having to maintain Scala.js builds and don't want to have to type the JVM suffix every time I'm changing projects, etc.)

This doesn't compile in SBT 1.0 because Project doesn't have a copy method now.

Okay, let's check the migration guide.

Many of the case classes are replaced with pseudo case classes generated using Contraband. Migrate .copy(foo = xxx) to withFoo(xxx).

Cool, let's try it.

build.sbt:100: error: value withId is not a member of sbt.Project
  .jvmConfigure(_.withId("core"))
                  ^

So I asked on Gitter and got crickets.

The links for the 1.0 API docs actually point to something now, which is nice, but they're not very helpful in this case, and trying to read the SBT source gives me a headache. I'm not in a rush to update to 1.0, but I'm going to have to at some point, I guess, and maybe some helpful person will have answered this by then.