I think that is correct.  If you uncheck the option, you should end up installing only the 64 bit version.

There shouldn't be any need to alter your existing Runtimes.  I am using my old Runtimes from P4, P5, P7, and P8 with Pro 2012, in addition to some custom Runtimes for special projects or categories.  Just import the existing Runtimes using the library.

Unless you mean the Runtimes are on an external hard drive which may not always be attached.    I'm not sure whether it might be better to relocate those or not.

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Cage can be an opinionated jerk who posts without thinking.  He apologizes for this.  He's honestly not trying to be a turkeyhead.

Cage had some freebies, compatible with Poser 11 and below.  His Python scripts were saved at archive.org, along with the rest of the Morphography site, where they were hosted.