Why we are not able update the Start Date(From Assignment Date) while creating the customer bank a/c

Summary:

Why we are not able update the Start Date (From Assignment Date) while creating the customer bank account if entered incorrectly

Content (required):

In Manage Customer page, while creating/updating bank account the start date is picking up default as system date. Its getting automatically greyed out after creating the bank account. As per business request is there any other way to update this start date. Can someone please let us know why we are not able to change the assignment start date. Is this a product limitation and any enhancement request already in place for this ?

Version (include the version you are using, if applicable):