Well, poking around I found an existing Mergelayers script - prolly about the same as @Helvetosaur 's, maybe I even stole it, but for the sake of variety, here you go -
MergeLayers.py (1.2 KB)
The other one should also be possible.
I don’t know if this is it but maybe -
MergeIdenticallyNamedLayers.py (1.4 KB)
Testing is guaranteed cursory.
To use the Python script use RunPythonScript, or a macro:
_-RunPythonScript "Full path to py file inside double-quotes"
-Pascal