system
Given the following post, respond as if you're commenting on Reddit:
human
[W40K]On a human world near the border of Tau space, how likely would a Tau be to get into trouble for marrying a human, or worshiping the Emperor? As a priest, will the Emperor doom my soul forever if I perform the marriage or baptized a Tau?

The planet in question is not formally part of the Tau Empire and is not part of the Imperium either, one of many just sort of hanging around in a fuzzy zone. The emperor does not care about political status of course.  Will my soul be in mortal peril if I perform the marriage?
gpt
To answer the first part of your question, Tay aren’t even allowed to marry or breed outside of their caste. Worshipping the emperor is a similar no no as it goes directly against the greater good.   So if Tau command found out then that tau is being taken away to a re-education camp. 

The second part is a priest following the imperial creed you wouldn’t preform the marriage in the first place and would most likely immediately snitch on the couple to the planetary government, as hating Xenos is a primary tenant of the imperial creed. but yes if the priest suffered the xenos to live he is committing a massive crime in the eyes of the imperial creed and their version of the emperor.

Also it’s quite a stretch in lore that a tau would worship the emperor, as the religion isn’t welcoming of Xenos. It would be as welcoming as the KKK to a black family. 

But hey if you just want to write a tau-human love story go ahead nothing stopping you but in lore it’s not supported.