In WRS 2.2 there's no way to POST a CR but you can customise the existing endpoint, this would be very limited without further customisations in terms of the CR soft-type, process associations, affected objects and end items etc
In codebase\rest\ptc\domain\ChangeMgmt\entity edit the file ChangeRequests.json.
Add CREATE to operations like this "operations": "READ,UPDATE,CREATE" and the functionality will be exposed immediately.
Alternatively, you can use a 'Create-Objects' webject, which can be invoked using REST /InvokeIETask.
<ie:webject name="Create-Objects" type="ACT">
<ie:param name="instance" data="<%=com.infoengine.au.NamingService.getVMName()%>" />
<ie:param name="CONTAINER_REF" data="<%=containerRef%>"/>
<ie:param name="FIELD" data="name='MC_initial_creation'"/>
<ie:param name="GROUP_OUT" data="output"/>
<ie:param name="TYPE" data="<%=CRSoftType%>"/>
</ie:webject>
