I believe in theory the Mendix Cloud team could do this form you, but I don't think they should as in that case it would be a global setting for your whole app and not just this specific endpoint.
I see two possible solutions:
- Preferred: Have the people managing the endpoint you're connecting to produce a self-signed cert for the correct hostname. This should not be hard to do.
- Create your own Java action which calls the endpoint, in this case you have full control over the way the cert is checked. I would advice against this for multiple reasons. It's not a very good case for introducing custom Java code in your project, you introduce a security risk and you are not testing all aspects of the implementation that would be used in production.