Rav Yoni Rosensweig wrote these guildelines for postponed Tisha Bav for this year (translated by Benjy Singer from IsraelK):
This is a short list of Halachas for Tisha B’av which falls out on Shabbat and is postponed to Sunday. When there different opinions I brought them, and the final opinion is that which I agree with.
* Some say that on Shabbat, from midday, one may only learn that which is permissible to learn on Shabbat, but others allow learning anything because to do otherwise would be to exhibit signs of mourning in public on Shabbat.
* Some prohibit marital relations on this Shabbat, but other believe that none of the prohibitions of Tisha Ba’v apply.
* אב הרחמים is said in Shacharit, but צדקתך צדק is omitted in Mincha.
* Some believe that Seuda Mafseket should be a modest meal, but most opinions hold that since it is on Shabbat it can be as plentiful as one would like. Still, it is best to eat it with one’s own family, rather than sitting with friends in mirth and joy and enjoying the meal.
* The prohibitions on eating and drinking, washing and lathering (with oil), begin at sundown.
* Regarding switching from Shabbat shoes to Tisha B’av shoes, some write that after “Barchu” at Maariv the public removes its shoes (and the chazzan does it before Barchu so as not to get confused). However, if this is the custom one goes by, Tisha B’av shoes cannot be brought to shul beforehand because that would constitute preparing from Shabbat to Tisha B’av, and therefore one would have to walk home barefoot (though if one is worried about hurting his feet on the way home it is permissible to wear leather shoes). However, a different opinion holds that one waits 25 minutes after sundown, says ברוך המבדיל בין קודש לחול, then switches shoes, and comes to shul for Maariv.
* On Motzei Shabbos we say the bracha on the candle. On Motzei Tisha B’av we say Havdala on the cup. We do not make the bracha on spices at all.
* There are many different opinions about what pregnant or nursing women should do on Tisha B’av, and due to the nature of this list it would be too cumbersome to mention them all. In practice, I rule that they do not have to fast, and especially this year when the fast doesn’t come out on its original date. And they need to make havdala before they eat, and they should make it on natural juice, tea, coffee, milk or root beer.
* If one has a Brit on Tisha B’av, some say that the father, sandak and Mohel are all exempt from fasting after midday; and same goes for a Pidyon Haben held on exactly the 31st day, that the Kohen and the father are exempt after midday. However, some hold that today our minhag is to fast all the way through.
* On Motzei Tisha B’av, some hold that havdala is made on wine, and somme hold it should be made on other liquids (mentioned above), and the best thing would be to make havdala on wine and give some to a child less than Bar mitvah or Bat mizvah age.
* On Motzei Tisha B’av one is still prohibited to drink wine or eat meat until dawn of the next day, but all other prohibitions fall away immediately.