Re hello Saguaros,
Yes i'm using Uber template. Normally I made every suggestion of update.
I had a look in the T3 plug-in, the version was until 2015 (written beside the copyright), so I've dowloaded the last version of T3 framework (until 2017) here, and installed it.
I made the same changes in the megamenu configuration, then changed some menu setting, publishing, unpublishing, and the submenu width in the megamenu configuration was saved : )
So your suggestion seems to work fine for now.
Thank you very much Saguaros and Pavit for your time and help !