Yes, but you need to do it using Windows APIs because there are no integrated Plus! script objects or commands to dynamically change it...
The <help> tag is used to display a tooltip. Tooltips can be made and changed using some Windows APIs. There are some scripts and snippets on the forums which do this. And there is even a library which makes things easy if you aren't that experienced with the Windows API.
Search the script subforum with "tooltip" and you'll bound to find what you're looking for.
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