Since the file is not all that long...
[?xml version="1.0" encoding="utf-8" ?]
[PlanetDescriptions]
[DataChecksum NoParse="1"]
[Ignore]Name,ColorScheme[/Ignore]
[/DataChecksum]
[!--
[PlanetDescription]
[Name]BarrenNoPotential[/Name]
[ColorScheme]Barren[/ColorScheme]
[UsableElevationRange]0.4,0.8[/UsableElevationRange]
[EnhancementPotential]0[/EnhancementPotential]
[ClassRange]1,7[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]BarrenWithPotential[/Name]
[ColorScheme]Barren[/ColorScheme]
[UsableElevationRange]0.4,0.75[/UsableElevationRange]
[EnhancementPotential]10[/EnhancementPotential]
[ClassRange]1,7[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]MidClassNoPotential[/Name]
[ColorScheme]MoreWater[/ColorScheme]
[UsableElevationRange]0.40,0.7[/UsableElevationRange]
[EnhancementPotential]0[/EnhancementPotential]
[ClassRange]8,12[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]MidClassWithPotential[/Name]
[ColorScheme]MoreWater[/ColorScheme]
[UsableElevationRange]0.40,0.7[/UsableElevationRange]
[EnhancementPotential]10[/EnhancementPotential]
[ClassRange]8,12[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]EarthlikeNoPotential[/Name]
[ColorScheme]Earthlike[/ColorScheme]
[UsableElevationRange]0.4,0.7[/UsableElevationRange]
[EnhancementPotential]0[/EnhancementPotential]
[ClassRange]13,36[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]EarthlikeWithPotential[/Name]
[ColorScheme]Earthlike[/ColorScheme]
[UsableElevationRange]0.35,0.7[/UsableElevationRange]
[EnhancementPotential]10[/EnhancementPotential]
[ClassRange]13,36[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]AfricalikeNoPotential[/Name]
[ColorScheme]DesertCenter[/ColorScheme]
[UsableElevationRange]0.35,0.55[/UsableElevationRange]
[EnhancementPotential]0[/EnhancementPotential]
[ClassRange]13,18[/ClassRange]
[/PlanetDescription]
--]
[PlanetDescription]
[Name]Testing123[/Name]
[ColorScheme]Earthlike[/ColorScheme]
[UsableElevationRange]0.35,0.7[/UsableElevationRange]
[EnhancementPotential]17[/EnhancementPotential]
[ClassRange]10,15[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]Eden[/Name]
[ColorScheme]PerfectPlanet[/ColorScheme]
[UsableElevationRange]0.35,0.7[/UsableElevationRange]
[EnhancementPotential]10[/EnhancementPotential]
[ClassRange]16,100[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]OceanPlanets1[/Name]
[ColorScheme]OceanPlanet[/ColorScheme]
[UsableElevationRange]0.7,0.99[/UsableElevationRange]
[EnhancementPotential]20[/EnhancementPotential]
[ClassRange]5,9[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]DesertPlanets1[/Name]
[ColorScheme]DesertPlanet[/ColorScheme]
[UsableElevationRange]0.3,0.5[/UsableElevationRange]
[EnhancementPotential]40[/EnhancementPotential]
[ClassRange]0,7[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]IcePlanets1[/Name]
[ColorScheme]IcePlanet[/ColorScheme]
[UsableElevationRange]0.3,0.5[/UsableElevationRange]
[EnhancementPotential]20[/EnhancementPotential]
[ClassRange]0,8[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]JunglePlanets1[/Name]
[ColorScheme]JunglePlanet[/ColorScheme]
[UsableElevationRange]0.29,0.40[/UsableElevationRange]
[EnhancementPotential]30[/EnhancementPotential]
[ClassRange]4,7[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]RockAndSandPlanet[/Name]
[ColorScheme]RockPlanet1[/ColorScheme]
[UsableElevationRange]0.75,0.99[/UsableElevationRange]
[EnhancementPotential]20[/EnhancementPotential]
[ClassRange]0,6[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]JustRockPlanet[/Name]
[ColorScheme]RockPlanet2[/ColorScheme]
[UsableElevationRange]0.5,0.7[/UsableElevationRange]
[EnhancementPotential]10[/EnhancementPotential]
[ClassRange]0,3[/ClassRange]
[/PlanetDescription]
[PlanetDescription]
[Name]RedPlanet[/Name]
[ColorScheme]RedPlanet1[/ColorScheme]
[UsableElevationRange]0.6,0.75[/UsableElevationRange]
[EnhancementPotential]10[/EnhancementPotential]
[ClassRange]0,3[/ClassRange]
[/PlanetDescription]
[/PlanetDescriptions]
All you have to do is copy it into Notepad and do an Edit-Replace to change the [ back to < and the ] back to >.
Then save it as PlanetDescriptions.xml, overwriting the messed up one.
Next time, use the Mods folders, that is why they are there.
(or at the very least, save a copy of the original in a different folder)
On a different note:
Main Entry: un·wit·ting
Pronunciation: -'wi-ti[ng]
Function: adjective
1 : not knowing : UNAWARE
2 : not intended : INADVERTENT
One can not unwittingly mod a file. It has to be opened, then changed, then saved.
This is all done with forethought and possibly with malice.
Possibly with ignorance, as well. But that, after all, was covered in your title.
The mistake was unwitting, perhaps, but not the modding.