Thread:Phoenix Red/@comment-44199553-20191024021145/@comment-6421408-20191024050927

The movie's novelisation explains that the Tenseigan can be acquired when an Ōtsutsuki is implanted with the Byakugan of a Hyūga. The transformation takes several days to complete. As the transformation advances, Toneri experiences increasingly painful pulsations in his eyes that subside with rest.

That is the only canonical way of achieving the Tenseigan I believe. If you want to achieve the Tenseigan is some other way, you will have to come up with something of your own with reasonable explaination, I can't help on that one.