Everything is explained in the
Lua manual.
You can't, and I do not plan to allow this.
Again, read the documentation... In excess of being able to change the avatar names color, you now can change the contents of the "marked" column for each avatar (up to three ASCII characters or any special UTF-8 symbol may now be used in this column, and the color for them can be set to anything fancying you), and you can set a tool-tip (with any arbitrary text) for each avatar line.
The OnRadar() callback was also improved, and is now called for every new entry added to the Radar (so that you can change the avatar data with the above new features as soon as it gets added in the Radara floater list). There is also a new OnRadarSelection() callback.