Hi there and happy new year,
the chainloading was introduced at some point to load a very primitive connectivity for a synfire chain. When set to "true", what it will do, is to increase the weight of all connections from cells in pattern0 to cells in pattern1 ... then from pattern1 to pattern2 ...
Since this function is not actively maintained it might be purged in one of the future version of Auryn. It is mostly still there for API compatibility. So I would say your usage is correct.
The overwrite argument specifies if all weights which are touched by the call are incremented by the second argument (and therefore allowed to pile up) or set to the second argument.
Finally one word on loading multiple patterns. Although your code should work, you can also load multiple patterns from a single file. The list of NeuronIDs in the textfile just needs to be interrupted by two empty lines. Indices after such a "paragraph" will be interpreted as a new pattern. See also http://www.fzenke.net/auryn/doku.php?id=manual:pat
I hope that helps.