In Naruto to awaken the rinnegan is much more difficult than arousing the tenseigan. To awaken the tenseigan it is necessary to implant the byakugan of a hyuuga in an ootsutsuki of the moon, by that logic to implant cells of an ootsutsuki of the moon in a hyuuga with byakugan would also work, as well as to implant the cells of hashirama (Ashura) in madara (Indra ) originated the rinnegan, and also the same would be valid if the eien no mangekyou of madara (Indra) in hashirama (Ashura) was implanted.
The difference in difficulty lies in the fact that the rinnegan requires the EIEN NO MANGEKYOU SHARINGAN of a reincarnation of INDRA along with the cells (chakra) of an ASHURA reincarnation, while the tenseigan required a byakugan of a hyuuga and the cells (chakra) an ootsutsuki of the moon.
The interpretation that it is only possible to awaken the rinnegan with the reincarnations of INDRA and ASHURA occurred coincidentally by the fact that only madara, Indra's reincarnation, managed the rinnegan by implanting hashirama cells (Ashura's reincarnation), and later, sasuke who is also Indra's reincarnation along with the other "half" Ashura won by the hagoromo.
But my opinion is that this did not happen because they are reincarnations, but rather because they managed to reach the eien no mangekyou sharingan level. In the story of Naruto the only ones that reached that level were Indra, Madara and Sasuke, so Madara reached that level and got Senju cells and Sasuke also reached that level and got his own chakra of the hagoromo, thus getting them both to wake the rinnegan.
I have already seen many asking why Obito did not awaken the rinnegan, the fact that Obito did not awaken the rinnegan was not because he was not a reincarnation of INDRA, but because he never achieved the level of EIEN NO MANGEKYOU SHARINGAN, besides the fact have only one sharingan.
I see that Sarada has the possibility of awakening the rinnegan if she implanted the hashirama cells and if he reached the level of the eien no mangekyou sharingan.