I'm unsure what you mean by a custom schema for lxtgaz files. Are you referring to the output generated by LocateXT? Currently, LocateXT lxtgaz files require a location (in LAT/LONG form), a name, and--optionally--keywords. There is a step by step process that can be followed when using LocateXT in Desktop or ArcGIS Pro, or you can upload a list of names and LAT/LONGS from a structured document (.xlsx, .csv etc) and create an lxtgaz file from that document. Note, the lxtgaz file will need the keywords manually added to each location.
Let me know if you have additional questions!