The runtime isn't part of the programme as it stands, it's just a folder that the programme accesses and as such has nothing to do with registry entries. Yes you will obviously have to re-install your main Poser programme but that isn't what the original question was.

The runtime "can" be copied as a complete folder and put somewhere safe, you can then uninstall Poser and manually delete the folders it leaves behind, you must delete those folders as well to do a completely clean re-install,  then do a complete re-install and when that's done you delete the runtime from the install and replace it with the one you kept safe. This has no effect on registry entries or anything else and it works just fine, I've done it before and if I'm not mistaken there is instruction on doing this on the CL web site.

Injustice will be avenged.
Cofiwch Dryweryn.