ArcGIS Pro 2.9 API Reference Guide
CustomDefaultToolbox Property

ArcGIS.Desktop.Core Namespace > GeneralOptions Class : CustomDefaultToolbox Property
Gets and sets the path to a toolbox to use as the default toolbox for new projects
Syntax
public string CustomDefaultToolbox {get; set;}
Public Property CustomDefaultToolbox As String
Remarks
Set DefaultToolboxOption to OptionSetting.UseCustom after setting the CustomDefaultToolbox (to use the CustomDefaultToolbox with newly created projects). Attempting to set the DefaultToolboxOption to UseCustom before CustomDefaultToolbox contains a valid path will be ignored.
Conversely, attempting to set the CustomDefaultToolbox back to null or empty string will be ignored if DefaultToolboxOption is currently set to UseCustom. The DefaultToolboxOption must be changed to UseDefault first.
Requirements

Target Platforms: Windows 11, Windows 10, Windows 8.1

See Also

Reference

GeneralOptions Class
GeneralOptions Members