You can't programmatically set the tooltips in the view XSLTs. You might be able to add some code to the XSLT that does this but we couldn't figure out a way to do it and it's probably a deep dive with no certainty of finding the treasure.
I recommend just having a calculated value somewhere in your form that displays guidance text depending on which textbox the user clicks on. That's easy to do. The guidance text can change. It won't be a tooltip however and it will require code to get the context or injecting the qRules common code library into your form and using a rule to call it (qRules contains the functions to do this).