You can always disconnect the subform from its RecordSource before updating the table(s), then reconnect it:
Private Sub Command_PopulateTable_Click()
Dim strRecordSource As String
strRecordSource = .RecordSource
' Call here the macro of function that populates the table(s).
.RecordSource = strRecordSource
-Command_PopulateTable is the name of the Command Button used to populate the table(s).
-SubFormControl is the name of the SubForm/SubReport control.