The druid spell Reincarnate says "The reincarnated creature recalls its former life and experiences. It retains the capabilities it had in its original form, except it exchanges its original race for the new one and changes its racial traits accordingly."
Tasha's Cauldron of Everything includes optional rules for "Customizing your Origin" (pp. 7, 8), which allows you much more flexibility in assigning the ability score modifiers, languages, proficiencies, and personality obtained as "racial traits".
In the case that Tasha's optional rules are in force, and with DM approval, what happens to a character that is the subject of the reincarnation spell?
Are the original choices made at character creation 'imported' to the new form?
Are the new racial traits able to be modified freely, as the old ones were at character origin?
Or does the new form possess the 'standard' racial traits of its race, since Tasha's specifically applies to character creation?
There are several related question on how reincarnation affects racial traits and feats, but none specifically address the customization option in Tasha's:
Do you lose racial feats when Reincarnated out of your race?
How does reincarnation affect feats and ability score increases?
Best Answer
Ask your DM.
Using options from Tasha’s in the first place is going to be up to the DM, so the outcome of a spell that wasn’t written to work with Tasha’s racial options is going to be up to the DM.
RAW, reincarnate obviously references the “non-customized origin” version of those races, since it is a Player’s Handbook spell.