Any preferences which can be set within Geneious Prime can also be set from the geneious.properties file which can be found in the Geneious Prime installation directory. On MacOS this file is located in Geneious.app/Contents/Java (R9 and above), or Geneious.app/Contents/Resources/app (R8 and earlier).
Some examples are present in the file already- remove the hashes from the start of the lines and modify the values to use them. If you need to find out how to set other preferences using this file, please use the Support button in the Geneious toolbar to request help.
It is also possible to turn off access to all external services by editing this file (this is not possible via the preferences inside Geneious). This includes access to NCBI, Uniprot, Geneious plugin download, submission of error reports, support requests and usage tracking.