If you want to replace all PropertyNumber controls with a larger text box - you could create your own rendering control like this:

public class MyPropertyNumberControl : EPiServer.Web.PropertyControls.PropertyTextBoxControlBase
{
    public override void ApplyControlAttributes(System.Web.UI.WebControls.WebControl control)
    {
        base.ApplyControlAttributes(control);
        control.SkinID = "Size100";
    }
}

And register by either initalization module, global asax or web.config. All described here:

http://blog.mathiaskunto.com/2012/03/05/being-friends-with-the-propertycontrolclassfactory-or-101-ways-to-change-episerver-built-in-property-appearances/