Apply a product
To apply a product, use the ApplyProduct method of the IProductLineModel object.
public void ApplyProduct(ICommandContext c, ICommandParams p)
{
    IProductLineModel productLineModel = c.App.Workspace.CurrentProject.ProductLineModel;
    //Apply the product with the specified name
    productLineModel.ApplyProductBy("ACC-0011");
    //Apply by product
    IProduct product = ...
productLineModel.ApplyProduct(product);
}