Can I loop over properties in ARM templates?

Indeed you can! Copy does work with properties!

Create a parameter or variable like this (this example will use parameter array):

"lbRules": {
  "type": "array",
  "defaultValue": [
    {
      "name": "httpPort",
      "frontendPort": "80",
      "backendPort": "80",
      "protocol": "tcp"
    },
    {
      "name": "customAppPort",
      "frontendPort": "8080",
      "backendPort": "8888",
      "protocol": "tcp"
    },
    {
      "name": "httpsPort",
      "frontendPort": "443",
      "backendPort": "443",
      "protocol": "tcp"
    }
  ]
}

Use this parameter in the Loadbalancer resource using copy like this that will create that many probes and rules that you defined in your parameter array:

{
  "apiVersion": "[variables('lbApiVersion')]",
  "type": "Microsoft.Network/loadBalancers",
  "name": "[parameters('myLoadBalancer')]",
  "location": "[parameters('computeLocation')]",
  "dependsOn": [
    "[concat('Microsoft.Network/publicIPAddresses/',concat(parameters('lbIPName'),'-','0'))]"
  ],
  "properties": {
    "frontendIPConfigurations": [
      {
        "name": "LoadBalancerIPConfig",
        "properties": {
          "publicIPAddress": {
            "id": "[resourceId('Microsoft.Network/publicIPAddresses',concat(parameters('lbIPName'),'-','0'))]"
          }
        }
      }
    ],
    "backendAddressPools": [
      {
        "name": "LoadBalancerBEAddressPool",
        "properties": {}
      }
    ],

    "copy": [
      {
        "name": "probes",
        "count": "[length(parameters('lbRules'))]",
        "input": {
          "name": "[concat(parameters('lbRules')[copyIndex('probes')].name,'Probe')]",
          "properties": {
            "intervalInSeconds": 5,
            "numberOfProbes": 2,
            "port": "[parameters('lbRules')[copyIndex('probes')].backendPort]",
            "protocol": "[parameters('lbRules')[copyIndex('probes')].protocol]"

          }
        }
      },

      {
        "name": "loadBalancingRules",
        "count": "[length(parameters('lbRules'))]",
        "input": {
          "name": "[parameters('lbRules')[copyIndex('loadBalancingRules')].name]",
          "properties": {
            "frontendIPConfiguration": {
              "id": "[concat(resourceId('Microsoft.Network/loadBalancers', parameters('myLoadBalancer')),'/frontendIPConfigurations/LoadBalancerIPConfig')]"
            },
            "frontendport": "[parameters('lbRules')[copyIndex('loadBalancingRules')].frontendport]",
            "backendport": "[parameters('lbRules')[copyIndex('loadBalancingRules')].backendport]",
            "enableFloatingIP": false,
            "idleTimeoutInMinutes": "5",
            "protocol": "[parameters('lbRules')[copyIndex('loadBalancingRules')].protocol]",
            "backendAddressPool": {
              "id": "[concat(resourceId('Microsoft.Network/loadBalancers', parameters('myLoadBalancer')),'/backendAddressPools/LoadBalancerBEAddressPool')]"
            },
            "probe": {
              "id": "[concat(variables('lbID0'),'/probes/', parameters('lbRules')[copyIndex('loadBalancingRules')].name,'Probe')]"
            }
          }
        }
      }
    ],


    "inboundNatPools": []
  },

  }
}

More info can be found here:

• https://docs.microsoft.com/en-us/azure/azure-resource-manager/resource-group-create-multiple#property-iteration
• https://docs.microsoft.com/en-us/azure/azure-resource-manager/templates/copy-properties

You can only apply the copy object to a top-level resource.

You cannot apply it to a property on a resource type, or to a child resource.

"resources": [
  {
    "type": "{provider-namespace-and-type}",
    "name": "parentResource",
    "copy": {  
      /* yes, copy can be applied here */
    },
    "properties": {
      "exampleProperty": {
        /* no, copy cannot be applied here */
      }
    },
    "resources": [
      {
        "type": "{provider-type}",
        "name": "childResource",
        /* copy can be applied if resource is promoted to top level */ 
      }
    ]
  }
] 

Source of Quotation: Deploy multiple instances of resources in Azure Resource Manager templates

You can loop over properties in ARM Template ONLY IF the copy object is applied to a top-level resource, which is in your case the "Microsoft.Network/loadBalancers", but that will also create multiple copy of the said resource.

If this is not what you want to achieve, I would recommend you to keep your existing way until ARM Template support copy object to property on a resource type in the future.