The JAX-RS tooling should provide more content assist, including creating methods annotated with @GET, @POST, etc.. with sensible parameters (entity, id). Once the code is inserted (with valid import statements and proper formatting), the user should be able to quickly edit the parameter types or names.

See how the JDT classes are used in https://github.com/jbosstools/jbosstools-webservices/pull/232 to manipulate the existing code