Poseidon does not save the changeability of attributes (if 
true), so that attribute.getChangeability() returns null. 
However, true should be the default setting, so that a 
method should be changed in Transformer.java:

    
    private void transformAttr(Attribute attr, MofClass 
container) {
        if (elements.containsKey(attr)) return;
        
        StructuralFeature mofFeature;
        if (isOfType(attr, STEREOTYPE_REFERENCE)) {
            mofFeature = mof.getReference().createReference
(attr.getName(), getAnnotation(attr), 
ScopeKindEnum.INSTANCE_LEVEL, 
VisibilityKindEnum.PUBLIC_VIS, null, true);
            fqnsToResolve.put(mofFeature, getTagValues
(attr, TAG_REFERENCED_END));
        } else {
  /* HERE */          boolean changeable = 
attr.getChangeability() == null || 
ChangeableKindEnum.CK_CHANGEABLE.equals
(attr.getChangeability());
            mofFeature = mof.getAttribute().createAttribute
(attr.getName(), getAnnotation(attr), getScope
(attr.getOwnerScope()), VisibilityKindEnum.PUBLIC_VIS, 
getMultiplicity(attr.getMultiplicity(), 
OrderingKindEnum.OK_ORDERED.equals(attr.getOrdering
()), "true".equals(getTagValue(attr, TAG_UNIQUE, null))), 
changeable, "true".equals(getTagValue(attr, 
TAG_ATTR_DERIVED, null)));
        }
        elements.put(attr, mofFeature);
        mofFeature.setContainer(container);
        mapTags(attr, mofFeature);
    }