Jag leker lite med userkontroll, och har en label I en userkontroll som skall visa tiden.
Jag sitter dock fast när det hjäler property för att ändra textstorleken.
Normalt så gör jag ju så här:

 private Color colFColor;
public Color ClockBackColor
        {
            get
            {
                return colBColor;
            }
            set
            {
                colBColor = value;
                lblDisplay.BackColor = colBColor;
            }
        }

Hej, Jag tror du kan använda liknande:

private void ComboBox1_SelectedIndexChanged(System.Object sender, 
    System.EventArgs e)
{

    // Cast the sender object back to a ComboBox.
    ComboBox ComboBox1 = (ComboBox) sender;

    // Retrieve the selected item. 
    string selectedString = (string) ComboBox1.SelectedItem;

    // Convert it to lowercase.
    selectedString = selectedString.ToLower();

    // Declare the current size. 
    float currentSize;

    // Switch on the selected item.  
    switch(selectedString)
    {

            // If Bigger is selected, get the current size from the  
            // Size property and increase it. Reset the font to the 
            //  new size, using the current unit. 
        case "bigger":
            currentSize = Label1.Font.Size;
            currentSize += 2.0F;
            Label1.Font = new Font(Label1.Font.Name, currentSize, 
                Label1.Font.Style, Label1.Font.Unit);

            // If Smaller is selected, get the current size, in points, 
            // and decrease it by 1.  Reset the font with the new size 
            // in points. 
            break;
        case "smaller":
            currentSize = Label1.Font.SizeInPoints;
            currentSize -= 1;
            Label1.Font = new Font(Label1.Font.Name, currentSize, 
                Label1.Font.Style);
            break;
    }
}

Tack för det.