How to POST multiple declaration with AS3 without overwrite the existent ?

When you use AS3, you are declaring what final state you want the BIG-IP to be in when the declaration is applied. Don't think of using AS3 to add vips like you would run it 4 times to add 4 vips. You would want to define all the vips in the same declaration and post it at once. All the vips you want to add would be under the tenant: "{{Layer}} in your case.

In your case, add another {{nomeServizio}} to the same declaration.

See here, an example that has 2 virtual servers configured in the same declaration, all under one tenant

https://clouddocs.f5.com/products/extensions/f5-appsvcs-extension/latest/declarations/http-services.html#http-and-https-virtual-services-in-one-declaration