I haven't tested it, but this should be slightly simpler, and work better for subsequent review iterations (reviewing what changed once PR is updated):

    jj new main -m review
    jj new -m pr
    jj git fetch
    jj restore --from=big-change@origin .

Then keep squashing from `pr` to `review` as described in the article. When the PR gets a new version, rerun the last 2 commands.