IOS – make Chrome the default web browser in iOS

The crucial point to realize with the Guest account is that the User homefolder it creates, with preferences set in its /Library/Preferences folder, are wiped upon logout.

To effect changes, you need to make the changes (add the specific preference files) in the /System/Library/User Template/English.lproj folder. This folder contains the generic template User Homefolder structure used when creating a new user or the Guest User.

This page has details about how it is done in Snow Leopard, but it is applicable to Mavericks.

As of macOS Sierra there is no way to do this without a a little proxy program which you set as the default browser. This proxy program then dispatches the URL according to some settings and URL rules to the desired browser application.

Building on tron_jones's comment, I know of three available proxy programs you can use:

• LinCastor - Free: Doesn't seem to be currently maintained
• Choosy - Commercial: Very slick. Easy to setup. Great UI
• brosel - Open Source: Very lightweight. Setup only for people who are comfortable with the command line. (My own little contribution to this field...)

You would need one rule for the general case selecting Safari by default and a second rule for Youtube URLs which chooses Chrome. Specific setup depends on the tool you are using.