|"but what do I do with the non open-source Android?"|
Android is open source.
I don't understand why you need to install a third-party Wi-Fi adapter when there's one built in (unless it no longer works, in which case there's no need to disable it).
First you need an Android-compatible driver for the external Wi-Fi adapter. That could be a stumbling block. Check the website of that Wi-Fi adapter manufacturer.