Adding "promotional" text in preview image

Couldn’t find it on Hep section (it only mentions item descriptions), so asking here. Almost 2 years ago I added my first PHP item to CodeCanyon, and a few days ago it became the best-selling item of its kind (that is to say, it has most purchases when compared to competing items). At the same time, it’s the best-rated one.

I want to ask if it’s OK to modify preview image and add “promo” text/graphics (like some ribbon, or text “#1 PHP Licenser on CodeCanyon”). Needless to say, I will continue monitoring other scripts, so if another item outsells my product, I will remove such text from preview image immediately to ensure I’m not misleading buyers in any way.

I saw some authors doing it, so I guess it’s OK, but want to be sure.