I once did this in registry.xml with Image to Base64 | Base64 Encode | Base64 Converter | Base64 for the image and Text to Base64 | Base64 Encode | Base64 Converter | Base64 for the filename. But beware: if your customer updates the logo afterwards it gets reset by genericsetup once you reimport your profile.
The following would set the current Plone Logo SVG file:
<record name="plone.site_logo">
<value>filenameb64:cGxvbmVfbG9nby5zdmc=;data64: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</value>
</record>