Your approach to the script is correct, as conditions you may hardcode a certain age of the file to read, or number of records. You may also store the filetime of the last load into a variable and then do the comparison to find out, whether the current file is newer. The ELSE-condition may also contain an EXIT SCRIPT - thus no refresh.
Your code then may look like
LET sFile = 'YourFile'; IF dLastFileDate < FILETIME($(sFile)) THEN LOAD * FROM $(sFile); ELSE EXIT SCRIPT; END IF; LET dLastFileDate = FILETIME($(sFile));