nope, you need uninstall the old one and reinstall the new one. i know its pain, but no choice, because some monster are no more available in v13.
technically, they are no risk to just otherwise the old version with the new ones, but that let all the non used monster files in your data (that take place for nothing).
but as i say, they are no really risk to otherwrite, it replace meshes/textures and the esp with the new one
(if old version use .esm and .bsa, just delete them and install the new one)
better to start a new game too for avoid save corrupt or else
but my personal recommendation is to uninstall the old one and reinstall the new one, its pain, but its better if you not want CTD
macadamstreet
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