An insurer wants to add a new typecode for an alternate address to a basetypelist...

In the Guidewire InsuranceSuite framework, maintaining the integrity of the base configuration is paramount for ensuring a smooth upgrade path. This is achieved through a strict "extension-only" philosophy for out-of-the-box (OOTB) components. When a developer needs to modify a base typelist—like EmployeeAddress—they must understand the distinction between.tti (Typelist Interface)files and.ttx (Typelist Extension)files.

A .tti file defines the original structure and initial typecodes of a typelist. These files are considered "base" and should never be edited directly (making Option C incorrect). If a developer were to modify the base .tti, those changes would be overwritten during the next platform update. To safely add a new typecode to an existing base typelist, Guidewire requires the creation of a .ttx file with the exact same name as the base typelist (e.g., EmployeeAddress.ttx). This extension file tells the Guidewire metadata engine to merge the new entries with the existing ones at runtime.

Furthermore, Guidewire best practices for metadata extensions require specific naming conventions to prevent future "namespace collisions." While the .ttx file itself adopts the base name, the newtypecodeadded within that file should be suffixed with _Ext (e.g., alternate_Ext). This ensures that if Guidewire later releases a product update that adds an "alternate" code to the base EmployeeAddress typelist, the customer's custom code remains unique and does not conflict with the new base code.

Option B is incorrect because you do not create a new .tti with an _Ext suffix for an existing list. Option E is incorrect because .tix is not a valid Guidewire metadata file extension; the correct extension is .ttx. Therefore, Option D is the only choice that follows the correct file creation and naming convention protocols required by the Guidewire development lifecycle.