To modify a stored entity object, retrieve it, update it, then put it back to the entity store:

SimpleEntityClass sec = sda.pIdx.get("keyone");
sec.setSKey("skeyoneupdated");
sda.pIdx.put(sec);

Note that because we updated a field on the object that is a secondary key, this object will now be accessible by the secondary key of skeyoneupdated instead of the previous value, which was skeyone

Be aware that if you modify the object's primary key, the behavior is somewhat different. In this case, you cause a new instance of the object to be created in the store, instead of replacing an existing instance:

// Results in two objects in the store.  One with a
// primary index of "keyfive" and the other with primary index of 
//'keyfivenew'.
SimpleEntityClass sec = sda.pIdx.get("keyfive");
sec.setPKey("keyfivenew");
sda.pIdx.put(sec); 

Finally, if you are iterating over a collection of objects using an EntityCursor, you can update each object in turn using EntityCursor.update(). Note, however, that you must be iterating using a PrimaryIndex; this operation is not allowed if you are using a SecondaryIndex.

For example, the following iterates over every SimpleEntityClass object in the entity store, and it changes them all so that they have a secondary index of updatedskey:

EntityCursor<SimpleEntityClass> sec_pcursor = sda.pIdx.entities();
for (SimpleEntityClass sec : sec_pcursor) {
    sec.setSKey("updatedskey");
    sec_pcursor.update(item);
}
sec_pcursor.close();