There are several factors that need to be contemplated prior to a decision about how to deal with address book field additions.
1) Do new address fields need to be positioned between the stock field listings, or will new additions added/positioned at the bottom of the stock field listings be acceptable?
2) What checkout system is being utilized (standard, FLC, OPC, other?) and is there any chance that a merchant might switch from one system to another in the future?
3) What is the current number of address book field additions required, and what is the chance that additional ones will be required in the future?
4) Is the Import/Export of address book field additions desired, and if so, is the stock X-Cart Import/Export function desired, or can a merchant utilize a back-end option (such as cPanel) to accomplish the task, (or modify X-Cart code relating to the Import/Export function).
So, taking into consideration the broadest application (FLC + OPC + 1 (or more) address field addition/name change + allowance for leaving open the possibility for 1 or possibly 2 (fax & title?) future address field addition/name change), and given that Export/Import of the address book information is desired/required, then the following hard coding looks to be the best practice:
1) New database fields need to be added and arranged as one would want them arranged on the OPC page, and several files need to have the fields redefined.
2) Various template files/html forms will need to have blocks of code added for the field additions, and possibly be rearranged.
If positioning additional fields at the bottom of the stock address book field listings is acceptable, and the stock X-Cart function for the Import/Export of the new address book field additions is not required, then the recent X-Cart Address Book Improvement should do the job.
In between the X-Cart Address Book Improvement and what I presume to be the best practice of hard coding, depending on which above listed factors are required, there are some fairly simple code hacks that can accomplish the job.
Is all of this a fair assessment?
Reference discussions:
Adding company field in address book
http://forum.x-cart.com/showthread.php?t=58364&highlight=address_fields.tp l
Changes to address fields and layout in OPC
http://forum.x-cart.com/showthread.php?t=58832&highlight=address_fields.tp l