halacha - Is it allowed to prepare for maariv after Shabbos during the rabbinic tosefes Shabbos?

The time to daven maariv on Motzoei Shabbos is some period (where I am it’s around 15 minutes) after the stars come out. This period is called tosefes Shabbos.

In many shuls, the shaliach tzibbur puts on a talis for maariv. On Motzoei Shabbos, he does this before Shabbos goes out so as to be ready to start on time.

I understand that the amount of tosefes Shabbos from the Torah need only be a moment. The remainder of the (say 15 minute) period is rabbinic.

It seems therefore that there is no problem of Hachono (preparing for the next day) by putting on the talis, during the rabbinic tosefes Shabbos.

Is that right and how do we know it?