Damian-
You might want to investigate using Virtual Machines to support multiple versions of InDesign and XMPie.
Personally, I use VMware and I actually have about 9 different versions of InDesign (CS6 - CC 2021) and XMPie running on my laptop. Our customers are running several versions of the software and we have a handful of legacy applications which still need ongoing support. I've heard of other folks using Parallels on the Mac to support multiple version of InDesign.
The tricky part is the licensing. Since the license can only run on one machine (yes, each of the VMs is considered a machine in terms of licensing), so we have to deactivate and reactivate the keys when switching between environments. It is much easier and faster to switch environments if you purchase an additional license from XMPie Sales for both instances.
Be careful. There are NO downloads for CC 2018. I made the mistake of uninstalling it from my host machine a couple of years ago not realizing that I didn't have the installer files to reinstall into a fresh VM. I scoured the internet and contacted Adobe several times, but I never found a download link.
I strongly suggest to spend the time/effort/money to update/upgrade/migrate your legacy software to the most current version. There have been a boatload of new features added since 9.2.1.