When doing

sublist.commitLine('item')

, is there a way to stop

validateLine

event from firing?

Are you doing this within ClientScript?

Yes

Is the validateLine entrypoint defined in the same or a different script file? you could update the validateLine function to behave differently under a specific criteria

It's in the same file.

If you define it, it's going to trigger when a line is added. It's difficult to help you further without knowing what you're trying to accomplish, but you could simply update the function return true if the line isn't something that you want to validate.

function validateLine(context) {
  if (context.sublistId === "item") return true;
  if (/** some criteria met is invalid*/) return false;
  return true
}