Since Boruto doesn't yet have the ability to activate Karma at will so, he can't control its activation or deactivation. The only way for Boruto to activate Karma is with resonance, for now that is and he needs to be close to Kawaki as well.
The resonance is not only limited to Kawaki's karma,
She could obtain the mangekyou by killing someone close to her, going through a tramatic event or having deep emotions and we know this when sarada and Chocho followed the 7th hokage,Naruto. They followed him because Chocho though choji was not her dad and for sarada uchiha she wanted to see sasuke, Sarada's dad and when hearing where sasuke is sarada runs ...
This is an old question with old answers but now it looks incomplete. Tsunade appears in episode 72 of Boruto. You can see her here:
Boruto preview episode 72
She says she returns from a long trip in the same episode.
It really just depends on how much energy(chakra) the user has, as the vanishing rasengan is an "invisible" rasengan, considering the user Boruto isn't as "strong" as naruto or minato or Jiraiya.
But if Naruto could use the vanishing Rasengan it will surely be stronger than the rasengan
I might be wrong but I believe not, as Naruto and Sasuke are the reincarnations, their blood is still very much Uzumaki and Uchiha, but it is also said that Uzumaki and Uchiha are descendants from the Otsutsuki's, so it won't be known until she tries it on Naruto and Sasuke.
The Byakugan is referred to as the "All Seeing Eye", that can see through everything. The title of "All Seeing Eye" is something that can only exist in the realm of Gods, nothing below that. So, it is possible that the Otsutsuki Byakugan is more mystical, and possesses more powers than the Hyuga Byakugan that go beyond mere visual ...
This was done in order to make sure the Divine Tree was planted and the Chakra Fruit bore. And despite how crazy some Otsutsuki can be, I highly doubt that they would allow one to do something that could wipe out an entire planet without consulting the clan's leader. In fact, the main reason Otsutsuki operated in pairs (e.g Momoshiki-Kinshiki, Isshiki-...