.net - Reflection to add/set new custom attributes -

i trying figure way add new custom attribute @ runtime, realize might impossible settle adding customer attribute bit want try override/set size

my class this

public class poco1      <stringlength(15)>     property firstname string      property lastname string  end class 

i try like

dim lname stringlengthattribute = new stringlengthattribute(50)  dim last propertyinfo = this.getproperty(("lastname")).add(lname)