I'm not sure how you're setting the font for the nameplate, but font face and size changes do not require a ui refresh of any kind. They happen instantly when you use the :SetFont(...) function on the relevant control.
For example, if you type the following into the chat window:
Code:
/script ZO_ChatWindowTextEntryLabel:SetFont("ZoFontCallout")
The 'Say:' text will instantly change to something far too big. You can change it back with:
Code:
/script ZO_ChatWindowTextEntryLabel:SetFont("ZoFontChat")