How many aText snippets do you have?
AFAIK, there is no import tool for KM. However, there is a KM macro that will auto-create KM Macros using typed-string trigger, then doing an auto-expand. You might be able to adapt it for your needs.
See Create Text Expansions Macro
If you have many (>> 100) aText snippets that are more complex than a simple text expansion, then you might want to consider a dedicated tool like Typinator.