Different commerce payment paypal settings on dev and live sites
This is a question that has came in different shapes, I'd recommend reading https://drupal.stackexchange.com/a/118316/2322 answer to get a better understanding on how drupal commerce and rules store this information. I don't know how to access the UI form the action itself.

Instead of trying to modify specific values, what I'd do is to try to replace the whole rule object with the one you want using entity_import of the rules_config object, something like:

if (isset($configs['commerce_payment_paypal_ec'])) {
    $configs['commerce_payment_paypal_ec'] = entity_import('rules_config', '{ "commerce_payment_paypal_ec" : {
        "LABEL" : "PayPal Express Checkout",
        "PLUGIN" : "reaction rule",
        "OWNER" : "rules",
        "TAGS" : [ "Commerce Payment" ],
        "REQUIRES" : [ "commerce_payment" ],
        "ON" : { "commerce_payment_methods" : [] },
        "DO" : [
          { "commerce_payment_enable_paypal_ec" : {
              "commerce_order" : [ "commerce-order" ],
              "payment_method" : { "value" : {
                  "method_id" : "paypal_ec",
                  "settings" : {
                    "api_username" : "1",
                    "api_password" : "",
                    "api_signature" : "",
                    "server" : "sandbox",
                    "currency_code" : "EUR",
                    "allow_supported_currencies" : 0,
                    "txn_type" : "auth_capture",
                    "ec_mode" : "Mark",
                    "shipping_prompt" : "0",
                    "log" : { "request" : 0, "response" : 0 },
                    "ipn_logging" : "notification",
                    "receiver_emails" : "",
                    "reference_transactions" : 0,
                    "ba_desc" : "",
                    "show_payment_instructions" : 0,
                    "update_billing_profiles" : 1,
                    "enable_bml" : 0
                  }
                }
              }
            }
          }
        ]
      }
    }');
  }