Dee, Members, Krason,
My two cents here are to look at some other field mapping for this purpose. It might be painful but not impossible to do so. But then again, if you are just a soldier implementing a solution around the existing mapping in the past, then this discussion is a moot point and is just that - a discussion
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As we know, many a times, clients do not want the "already existing process, fields etc." to be touched. As the risk and expenses seem not worth it for the client.
So, the consultant has to get a feel of how the client would react, when faced with the idea of changing some existing configuration. Especially when the said config touches many important functionalities of the business.