Can I start Update row in After Insert trigger function?

Hello!

I need to log some row changes in a table with JSON format (row_to_json).

In the Before Update I can select the row into a column with JSON format.
And in After Update I can log this column into an archive table.
Plus I have the prior data in the JSON_TEXT field.

It's ok.

FUNCTION Before_Update
...
BEGIN
select row_to_json(thistable) into json_text_var
from thistable where id = OLD.id;
NEW.json_text = json_text_var;
RETURN NEW;
END;

FUNCTION After_Update
...
BEGIN
insert into logtable select 'thistable', NEW.id, NEW.json_TEXT;
RETURN NEW;
END;

But this technique isn't working in insert, because no OLD.id. and OLD row:

select row_to_json(thistable) into json_text_var
from thistable where id = ???.id;
No row!!! Only NEW.nn variables.

Only way if I call an update:

FUNCTION After_Insert
...
BEGIN
-- We try to update the log with a dummy update
-- This calls Before/After Update, logs + fills the json field
update thistable set json_text = json_text where id = NEW.id;
RETURN NEW;
END;

Does this cause problems?
If I call an Update in the Row before After_Insert finishes?

Version: PGSQL 9.6-11

Thank you for your help!

Best regards,
dd