I do not mean "can you do it", I mean can a commerical entity do it or allow you to do it.
The .pdf says specifically:
"Google’s anti-forking agreements, however, have inhibited operating system innovation through forking, ensuring that manufacturers and distributors are beholden to Google’s version of Android. Distributors know that any violation of an anti-forking agreement could mean excommunication from Google’s Android ecosystem, loss of access to Google’s must-have GPS and Google Play, and millions or even billions of dollars in lost revenue sharing. Thus, distributors avoid anything that Google might deem "fragmentation” — a term that Google “purposely leave[s]... very vague” and interprets broadly."
Their anti-forking provisions put them, in some ways, close to what MS got in trouble for in their anti-trust case (removing or threatening to remove OEM pricing from OEMs who sold non-Windows OSes).
Except you can and you don't need Google's permission to do it either. Many devices come with unlockable bootloaders, and all custom ROMs come without anything Google so you actually have to install Google apps manually should you want them.