Programmatically set default value for multiple row table webform element

YAML that looks like this:

- account: ''
  adjustment: '123'
  principal: ''
  interest: ''
  fee: ''
- account: ''
  adjustment: '456'
  principal: ''
  interest: ''
  fee: ''
- account: ''
  adjustment: '789'
  principal: ''
  interest: ''
  fee: ''
- account: ''
  adjustment: '012'
  principal: ''
  interest: ''
  fee: ''
- account: ''
  adjustment: '345'
  principal: ''
  interest: ''
  fee: ''

Can be done with code that looks like this:

#default_value] => Array
                (
                    [0] => Array
                        (
                            [account] =>
                            [adjustment] => 123
                            [principal] =>
                            [interest] =>
                            [fee] =>
                        )

                    [1] => Array
                        (
                            [account] =>
                            [adjustment] => 456
                            [principal] =>
                            [interest] =>
                            [fee] =>
                        )

                    [2] => Array
                        (
                            [account] =>
                            [adjustment] => 789
                            [principal] =>
                            [interest] =>
                            [fee] =>
                        )

                    [3] => Array
                        (
                            [account] =>
                            [adjustment] => 012
                            [principal] =>
                            [interest] =>
                            [fee] =>
                        )

                    [4] => Array
                        (
                            [account] =>
                            [adjustment] => 345
                            [principal] =>
                            [interest] =>
                            [fee] =>
                        )

                )

Adding a class in code:

[#attributes] => Array ( [class] => Array ( [0] => bold )

)
$elements['account'] = [
  '#type' => 'textfield',
  '#title' => t('Depository account'),
  '#readonly' => TRUE,
  '#attributes' => ['class' => ['row-label', 'bold']],
];
$elements['adjustment'] = [
  '#type' => 'textfield',
  '#title' => t('Prior month adjustment'),
  '#input_mask' => "'alias': 'currency'",
];