How do you manage variations in your BOM (Bill of Material)?

Preparing the bill of materials (BOM) is a crucial step before sending the assembly files to fabrication houses. The BOM plays a crucial role in the fabrication process, as fabrication houses need this data for various purposes like purchasing components or running it through silicon expert. Organizations follow their own template for BOM and may also be required to follow the guidelines of fabrication houses. 

Very often, different BOMs are required for the same design with some minor changes like different values for components, deletion of components as per regional compliances, etc. Making these changes in the BOM manually is a challenging task and is error prone. Creating unique designs and generating a BOM for each design is much more time consuming. 

How do you handle these BOM variations? Do you use any of the following methods to achieve this?   

1. Create separate designs and generate a BOM for each design. 
2. Generate one BOM for the core design and make the changes in the BOM manually. 
3. Create design variants within the same core design and generate BOMs for the variants.  

Do let us know if you use any other smart method for generating different BOMs.