Sorry, but there really is no way to determine gender based on a dump.
The most reliable way to determine gender is through ultrasound, behind the cloaca or vent, endoscopy or x-rays.
Behavior in the presence of another Meller's can also help distinguish gender. I don't see babies in your pics, so I hope you are not caging your two together. Or even real close to one another if in separate enclosures.
You may be lucky enough to catch some hemipenal bulge when a male basks or hunts or drinks. Also look for hemipenal plugs on perches, branches. Yet another indication of male.
No, I do not believe; despite what I've seen written; they "change sex".