After much brainstorming and head-scratching, a solution was finally found on how to replace these commands. There is another command in ArcMap called "Load Objects" that behaves almost the exact same way as the Simple Data Loader in ArcCatalog; the only difference is that after navigating to the location of the source feature class/table, the destination of the data is a layer chosen from the MXD. The command also allows you to map fields for loading.The interface I used is IObjectLoader. Since the schema of the destination feature class that I'm loading the data into is an exact copy of the source feature class, I didn't have to worry about using field mapping objects in code.Here's the examples I used in order to get the IObjectLoader.LoadObjects method working:C# exampleVBA exampleThe VBA example was pretty easy to change over to VB.NET and adapt to the variables I was already using in code. This thread got a lot of views, so I hope it helps people who are also searching for a solution!