I just tried the following:
Code:
/script SetNameplateKeyboardFont(string.format("%s|%d", "EsoUI/Common/Fonts/Univers67.otf", "26"),FONT_STYLE_SHADOW)
and it took effect immediately.
Two things,
1) (not the problem but...) I think it's better practice to use named constants rather than their values, as I've done above (i.e. FONT_STYLE_SHADOW rather than 1)
2) Your code snippet implies that it only runs in response the to the Player Activated event - are you calling a similar function after you've set your new font?