For the first issue,whatever you said is correct.we can change the MIME Type under Rest API Descripter from the Designer.
For Second issue,in case of Legacy Rest(RestV1),will get this problem.To resove this Problem,replace : and $ with some other Character (or) remove : and $ from schema $ref Property and definitions in Swagger.
Please find the below example.
Example:
Problem:
schema:
$ref: “#/definitions/JsonSchemaAPI.RestV1.Res.restV1Res:post$response”
definitions:
JsonSchemaAPI.RestV1.Res.restV1Res:post$response:
Solution:
schema:
$ref: “#/definitions/JsonSchemaAPI.RestV1.Res.restV1Res._post_response”
definitions:
JsonSchemaAPI.RestV1.Res.restV1Res._post_response:
#webMethods#Integration-Server-and-ESB#Flow-and-Java-services