We have an awful system written in ASP.NET 2.0 that we need to add some functionality to. The problem is that a certain product has UI features that have to be turned on for business initiated after a certain date (and others turned off), while the page has to appear the same for existing business.
I am pushing for a rewrite of the page for new business as I instinctively find the idea of date-based JavaScript UI switches, and the mixing of web controls for the old and new business to be "untidy" (for want of a better word).
Is the practice of having time-based UI features a widely accepted practice, and if not, what are the known risks of pursuing that course of action?