One thing that can be done with this file is to change the size of the text in different parts of the display.
It can also be used, as I learned in a post by Eep Quirk, to change the thickness of the glow that indicates the outlines of selected items when using the build editor.
The file is a text file, what an old timer like me might think of as an Ascii text file, whether that is precisely accurate terminology or not.
The file, in a default SL installationi on a Windows machine, lives in a folder called
C:\Documents and Settings\%%YourUserName%%\Application Data\SecondLife\user_settings
The file's name is settings.ini.
This file always has a bunch of settings in it, but there are additional settings that can be found through sneaky techniques searching for strings in the secondlife.exe file and other places. This is how the font size settings and the selected glow thickness settings were found.
The settings listed in this file produced by Second Life in it's normal mode of operation are in alphabetical order, or Ascii sort order, or some such very similar looking order.
Making modifications to the file would be a lot easier if it was known that the order of the settings didn't matter. Then you could just keep a simple text file with your customized additions and append it at the end. This could even be done with a batch file, and thus made as easy as clicking on a shortcut.
A batch file for this purpose might have just one line in it if the order that these setting appear is not a factor.
CODE
copy C:\Documents and Settings\%%YourUserName%%\Application Data\SecondLife\user_settings\settings.ini +C:\SLcustom\customization.ini C:\Documents and Settings\%%YourUserName%%\Application Data\SecondLife\user_settings\settings.ini
This tells the copy command to take the SL settings.ini file and add the text from a customization file with the settings you want to add and and copy the both of them back to a new SL settings.ini file in the right place for SL to use.
This might not work, I haven't tried it yet, I don't do much batch file writing anymore, surprise, surprise, but given how often one has to update SL, and thus lose custom settings.ini file entries, some kind of automizatioin of this sort might be worth pursuing.