Con Laravel Migration, ¿cómo cambiar el tipo de datos de una columna y actualizar sus datos existentes para que se ajusten al nuevo tipo de datos, sin utilizar consultas SQL sin procesar?

Así es como realicé esto:

El método arriba():

...
use App\User;

/**
 * Run the migrations.
 *
 * @return void
 */
public function up()
{
    // do the following steps in order:
    // 1- add a new column with the desired data type to the table
    // 2- fill the new column with the appropriate data
    // 3- delete the old column
    // 4- rename the new column to match name of the deleted column

    Schema::table('users', function(Blueprint $table)
    {
        // 1- add a new column with the desired data type to the table
        // note that after() method is used to order the column and works only with MySQL
        $table->boolean('is_suspended_new')->default(0)->after('is_suspended');
    });

    // 2- fill the new column with the appropriate data 
    // note that you may need to use data in the old column as a guide (like in this example)
    $users = User::all();
    if ($users) {
        foreach ($users as $user) {
            $u = User::find($user->id);

            if ($u->is_suspended === 'yes') {
                $u->is_suspended_new = 1;
            } elseif ($u->is_suspended === 'no') {
                $u->is_suspended_new = 0;
            }

            $u->save();
        }
    }

    Schema::table('users', function(Blueprint $table)
    {
        // 3- delete the old column
        $table->dropColumn('is_suspended');
    });

    Schema::table('users', function(Blueprint $table)
    {
        // 4- rename the new column to match name of the deleted column
        $table->renameColumn('is_suspended_new', 'is_suspended');
    });
}

El método down():

/**
 * Reverse the migrations.
 *
 * @return void
 */
public function down()
{
    // IMPORTANT NOTE:
    // because renaming (enum) column types is not supported in laravel 4.2 (as mentioned here https://laravel.com/docs/4.2/schema#renaming-columns)
    // so we will make some changes in the order of the steps as follows:
    // 
    // do the following steps in order:
    // 1- rename the exiting column
    // 2- add a new column with the desired data type and give it a name matches name of the existing column before renaming
    // 3- fill the new column with the appropriate data
    // 4- delete the old column

    Schema::table('users', function(Blueprint $table)
    {
        // 1- rename the existing column
        $table->renameColumn('is_suspended', 'is_suspended_old');
    });

    Schema::table('users', function(Blueprint $table)
    {
        // 2- add a new column with the desired data type to the table
        // and give it a name matches name of the existing column before renaming
        // note that after() method is used to order the column and works only with MySQL
        $table->enum('is_suspended', ['yes', 'no'])->default('no')->after('is_suspended_old');
    });

    // 3- fill the new column with the approprite data 
    // note that you may need to use data in the old column as a guide (like in this example)
    $users = User::all();
    if ($users) {
        foreach ($users as $user) {
            $u = User::find($user->id);

            if ($u->is_suspended_old == 1) {
                $u->is_suspended = 'yes';
            } elseif ($u->is_suspended_old == 0) {
                $u->is_suspended = 'no';
            }

            $u->save();
        }
    }

    Schema::table('users', function(Blueprint $table)
    {
        // 4- delete the old column
        $table->dropColumn('is_suspended_old');
    });
}