Rename or replace a field in drupal 8+ | Sămărtean Rareș

Steps

create a new field through the admin UI, as you normally would, with the new name
- It would be ideal if the new field was the same type as the old one, but custom conversions can be applied through smart SQL for different field types.
use these sql commands to transfer the data, replacing the field names
1. INSERT INTO node__field_new SELECT * FROM node__field_old
2. INSERT INTO node_revision__field_new SELECT * FROM node_revision__field_old
- If the column counts are not the same, use
  ...SELECT *, 'constant'...
  to substitute the missing columns.
  Adjust this SQL if the missing columns are in the middle, instead of at the end or beginning.

Notes

This also works for paragraphs if "node" is replaced with "paragraph" in the table names above.