In my opinion you are heading way down the wrong path by modifying components of mojoPortal. You are basically forking the code and once you do that it will be very difficult for you to keep up with upgrades and changes in mojoPortal and it will make it very difficult for me to provide support. You should keep all customizations in external projects and never change the core of mojoPortal. If you find yourself thinking you need to change the core you should let me know what you are trying to do and maybe I can tell you a way to do it without touching the core, or maybe I can think of something we can do in the core to make it easier to do what you want.
SiteSettings as of the the latest version has an ability for you to store your custom properties:
siteSettings.SetExpandoProperty(string keyName, string keyValue);
The only thing is there isn't currently a UI for your setting. I've been thinking of a way to make it possible to configure expando properties in a config file and then show them in the UI based on this but its not done yet. You could make a custom module that sets this setting very easily though.
For the redirect logic you should implement a signinhandler. There is also a web.config setting already existing that you can use to specify where to redirect after signin but as its in Web.config its global in a multi site installation it won't work well.
All of your work should be in your own external projects so that you can always do svn update to get the atest version of mojoportal.
You are right, although I removed that 188.8.131.52 script file I forgot to remove it from the project. I will do that today. There should always only be one file in the /Setup/applications/mojoportal-core/SchemaInstallScripts/mssql folder. After running this script it will run scripts from /SchemaUpgradeScripts/mssql that are of a higher version number.
Hope it helps,