Hi!
Are there ways to customize standart tooltip visualization?
I think there are no ways.
There is no way from BP, but you can simply use construction script and check if default TooltipText is empty, if not just creating simple widget with Text property exposed on spawn. Done 
https://i.imgur.com/EaqDjR1.png
There is a built-in method for this:
This will also maintain the life of the widget automagically. And you can feed it data via exposed parameters.
Obviously you can use also bindings, but they are not recommended due to performance cost. Get tooltip widget is triggered each hover of the widget which is fine, but for all other bindings like values / color it updates every single frame.
That’s why I rewrote widget binding system while I was working for Splash Damage. To avoid triggering it every single frame.
Glad we agree on that. I’ll just add that widget tooltips created by the bound function are NOT Garbage Collected - so that’s another thing to consider. Manually calling Collect Garbage will remove them from memory, though.
Rookie mistake