Is it possible to create a function for transactions that use more than one database? As an example, below is a transaction. Would it be possible to write a function defining each database/table, so that in the future I could simply plug in the fields and corresponding values and have them go to the correct database as part of that single call?

BEGIN;

  INSERT INTO ENTITY.entity (`first_name`, `last_name`, `create_time`, `update_time`, `hashID`)
           VALUES ('Lola', 'High', DEFAULT, DEFAULT, DEFAULT);
  INSERT INTO NUMID.numID_history (`id_status`, `id`, `criminal_status`, `charge`, `plea`, `sentence`, `create_time`, `update_time`, `hashID`)
           VALUES (000, 412056888, 0, NULL, NULL, NULL, DEFAULT, DEFAULT, LAST_INSERT_ID());
  INSERT INTO DOB.dob_state (`day`, `month`, `year`, `state_ID`, `stateID_status`, `create_time`, `update_time`, `hashID`)
           VALUES (1, 1, 1985, 34506028, 0, DEFAULT, DEFAULT, LAST_INSERT_ID());

COMMIT;


This might entail, for example, a function that inserts a value to a field only IF that field exists. For example, if the field "create_time" exists in all database.tables, then the value would be inserted in each of them. On the other hand, if "last_name" exists in only one of them, then it would be inserted only in that database.table.

I want a function to store which databases have which tables and use a set of fields that entails a union of all databases. Then when I insert values to fields, without me dictating which database gets what, the function should do that automatically.

Could I create such a function? How would I store it?
I believe I don't quite get what your question is about. The following function would insert those values, with the same values on fields like create_time, within a transaction, on multiple databases. Is this what you're looking for?

delimiter //
CREATE PROCEDURE yourdb.yourprocname (_first_name varchar(100), _last_name varchar(100), _create_time datetime, _update_time datetime,  _hash_id varchar(32),
  _id_status int, _id int, _criminal_status int, _day int, _month int, _year int, _state_id int, _state_id_status int)
begin
  START TRANSACTION;

  INSERT INTO ENTITY.entity (`first_name`, `last_name`, `create_time`, `update_time`, `hashID`)
    VALUES (_first_name, _last_name, _create_time, _update_time, _hash_id);

  INSERT INTO NUMID.numID_history (`id_status`, `id`, `criminal_status`, `create_time`, `update_time`, `hashID`)
    VALUES (_id_status, _id, _criminal_status, _create_time, _update_time, LAST_INSERT_ID());

  INSERT INTO DOB.dob_state (`day`, `month`, `year`, `state_ID`, `stateID_status`, `create_time`, `update_time`, `hashID`)
    VALUES (_day, _month, _year, _state_id, _state_id_status, _create_time, _update_time, LAST_INSERT_ID());

  COMMIT;
end//
delimiter ;


Example call:

call yourdb.yourprocname ('Lola', 'High', CURRENT_TIMESTAMP, ... etc)