To ensure that a chart is selected, you can add a statement to determine if a chart is active.
Sub ChartMods2()
If ActiveChart Is Nothing Then
MsgBox "Activate a chart."
Exit Sub
End If
ActiveChart.Type = xlArea
ActiveChart.ChartArea.font.name = "Calibri"
ActiveChart.ChartArea.font.FontStyle = "Regular"
ActiveChart.ChartArea.font.Size = 9
ActiveChart.PlotArea.Interior.ColorIndex = xlNone
ActiveChart.Axes(xlValue).TickLabels.font.bold = True
ActiveChart.Axes(xlCategory).TickLabels.font.bold = True
ActiveChart.Legend.Position = xlBottom
End Sub