I was thinking the same thing Ghostie ... based on this comment:

"@ an0malaus

the reason I want to disable is because .xmp enabled saved files are harder to work and re-work with in other versions of Poser .. :/"

This suggests to me that you are looking to get around the PMD (binary morph) files, which are saved in a compressed format, similar to a ZIP file so that the downloads are smaller.

There is a setting in the Preferences dialog (Edit > General Preferences), then click the Misc tab. In the "Save Files" section, UNCHECK the option to use external binary morph target, which will embed the morphs inside the character file like in the old days. You can also uncheck the "Use File Compression" option to save the library files in the old uncompressed format (in other words, CR2 instead of a zipped CRZ).

But, if you are actually asking about the XML files, what those do is save metadata that allows you to enter more specific search terms for the library. By default, Poser saves the XML files with basic information, like date created, date last modified, and file type. But you can add additional information in the Extended Details panel (see the pages from the manual above), or you can also choose the Scripts > Metadata Builder command to edit one or more files at the same time.

I think most people delete these XML files because "date created", "date modified" and File type don't really add much info. But I'm sure if people start using them and filling them out more, to help make library searches easier, Rendo would accept them.