It is not necessary to include all properties on an object when posting. If you are using the Lucity serialization objects and serializing them that will just happen automatically, but if you are manually building XML it is perfectly acceptable to include just the properties you want to update or insert. For example, a request can be inserted with the following body:
<Request><ProblemCode>test</ProblemCode></Request>
Which will insert a new request with the problem code = test.
What is required, however, is that whatever properties are included are listed in alphabetical order. Again, if you are using the Lucity Serialization objects this is irrelevant.