I think you are confusing namespaces and endpoints.
The namespace for a webservice should be set once, when creating the published webservice. It is a fundamental part of the webservice definition. Note expecially that the value of the namespace doesn't really matter, since the URL isn't actually used, called or opened anywhere.
The endpoint defines where the webservice is located. This can vary, for instance depending on whether you want to call a websrevice in a production, acceptance or test environment.
Based on your errors, I think you have published a webservice with a certain namespace, imported that into a different project, and then changed the namespace in the publishing project. Again, once you publish a webservice, you should define the namespace once, and then never touch it again. To fix this, re-import the webservice definition (wsdl) into you consuming project. Then, set the endpoint location to the endpoint of your publishing app node.
*Edit: According to your comments, you are mostly interested in downloading the ws-doc from a cloud node. As Achiel comments, this is disallowed on production environments for security reasons. Using the WSDL you can get from a development environment, your customer should be able to call your webservice using your production endpoint.
*Edit 2: The easiest way to have a third party consume your web service for a production cloud environment:
If you are using an older modeler that does not have the option above:
Regarding the "service name should be specified" error, we've also experienced this problem. For us the problem was in the IIS configuration; if you have IIS in front of your Mendix application, make sure you setup the URL Rewrite Rules correctly.
Make sure you have a Reverse Proxy rule as follows:
pattern: ^(ws/)(.*) and rewrite URL: http://localhost:8080/{R:1}{R:2}