if you take the basic kogito springboot archetype and you build it, go into the target folder, and in the generated-sources(?) you will see the generated code that kogito generates for you and your dmns.
take all that code and drag it into your src folder.
then delete the kogito plugin in your pom.xml
you now can modify that generated code.
i think there is a class called DecisionModels (it has been a while I can't remember)
there should be a collection called readers which is a list of readers or streams. kogito creates those streams from the dmn in the local resources folder.