Replacing the Loading Indicator
The OrchestraCMS Lightning components make use of the Lightning Design System Spinner. This can be overrridden by a developer using their own Lightning component. There is no OrchestraCMS specific code to the progress indicator.
To override the default indicator, use the loadingComponent parameter in a JSON string within the Developer Override String field on the Lightning component configuration in Community Builder.
{
"loadingComponent":"c:SampleLoadingSpinner"
}