You need to understand that your properties are actually changed during run time anyway when you run your application, based on form data (made by designer) or not — it does not matter.
You also need to read about properties and understand how they work. In brief, they are methods (getter/setter) providing interface and syntax mimicking reading of the field and assigning a value to the field, that is, from the point of view of the code using the object of your class, the property looks exactly like a field. So, what you need looks like this:
myObject : MyClass;
myObject =
myObject.MyProperty = newValue;
You certainly need to read a Delphi Pascal manual, pretty much from scratch and do simple exercises to make yourself comfortable before writing advanced applications.
—SA