Why doesn't the FormValidation library include the Tachyons plugin? Because of its absence, you cannot change messages using ajax requests.
Thank you for your feedback.
FormValidation is a 3rd-party commercial plugin and we are not sure about Tachyons usage with it.
For the validation error display styling, we use Bootstrap elements and some Metronic custom styling. Could you please explain us your requirements and we will try to show you direction how to implement it within existing Metronic features.