Can Curve Spline be used for an in game level editor.

[_Aka_]

What does includeOnRequestProcessing do since I seem to require this to have GetModule work.

Here is the documentation for that method:
https://api.curvyeditor.com/860/FluffyUn...m_Boolean_
The parameter means whether the method should also return modules that implement the IOnRequestProcessing interface. These modules have their inner workings different than other modules. "Normal" modules do their computation every time (when dirty) the generator is refreshed. IOnRequestProcessing modules do their computation only when requested by other modules.
The current list of such modules is:

• ConformPath
  
• InputSplinePath
  
• InputSplineShape
  
• ModifierMixPaths
  
• ModifierMixShapes
  
• ModifierPathRelativeTranslation
  
• ModifierTRSPath
  
• ModifierTRSShape
  
• ModifierVariableMixShapes
  

For simplicity sake, you can always set that parameter to true.

Edit* You said to modify the Destroy method in the CGMeshResourceLoader to add the custom scripts I needed. I'm having trouble allowing it to give access to my own namespace/scripts.

 
It is probably because you are using Curvy Splines with amsdef files. If so, short answer would be: remove the asmdef files in the ToolBuddy folder (recursively). The long answer would be: you need reference your code in the Curvy asmdef. More information here: https://docs.unity3d.com/Manual/ScriptCompilationAssemblyDefinitionFiles.html

Also if I'm to believe, I'll have to add every custom script I'd need these meshes to use into this right? Is there not an easier way to allow an entire prefab + its children to load into the Generator?

You can use whatever code you need in CGMeshResourceLoader.Destroy to specify what components to ignore. You can access obj.gameObject, and customize the stripping depending on the object. For example using Unity's tags.