I followed the instructions to the letter - download, expand, modify, flatten. Installed by double clicking the modified .pkg. Installed no problem. The install log only shows one error, to do with a bundle id with no name or something. In my case a lot of the components weren't installed because the correct components already existed (maybe because I'd run the 10.13.4 updater from the App Store previously, but per
@L Caputo's comment regarding the System Report, I did the combo update). I checked the install log and there were no recovery partition errors - in fact there was no mention of the recovery partition at all. I know in the past when I've updated from the App Store I've had errors in the log to do with the recovery partition, but not this time. I hope that helps but I don't pretend to understand the point you've made in your post.