Plugin override - Megamenu customization

Hi to everyone,

I looked around here and found nothing so far that solves my problem.
So maybe one of you can give me a hint.

I am using the megamenu with the t3 framework and I want to add a inside the tag of the megamenu.
I found where to add it but it is inside the "plugin/system/t3/includes/menu/megamenu.tpl.php" so I am not able to do an override.

Is there a solution so I can change that without loosing it after updating in the future?

Thx for the support.