Enigmatic Variations No.1171 – Who Am I? by Ifor

The preamble to WHO AM I? is quite intimidating.  There are two verses to be identified.  The first explains changes to two groups of three clues each, a phrase to be highlighted, and the answer to the titular question, which is to be written under the grid.  The second is given by extra letters in wordplay in 29 clues, and it identifies the number of the single normal clue and the rationale for the removal of the letters.  Got that?

The four lines of the first verse – the verse that provides the theme – are ‘Comment’ by Dorothy Parker:

Oh, life is a glorious cycle of song,
A medley of extemporanea;
And love is a thing that can never go wrong;
And I am Marie of Romania.

First line
In each of 2ac, 12dn and 27dn, LIFE in the answer is replaced by ‘a cycle of’ SONG (i.e. GSON, NGSO, or ONGS).

Second line
The diagonal, which is to be highlighted, reads EOPARMEXATEN, which is a ‘medley’ (anagram) of EXTEMPORANEA.

Third line
In each of 35ac, 1dn, and 5dn, an anagram of LOVE in the answer is ‘corrected’.

Fourth line
MARIE OF ROMANIA is to be written beneath the grid.

The extra letters from the wordplay read LOVE CURIOSITY FRECKLES AND DOUBT, which Parker lists as the four (the number of the normal clue) ‘things I’d been better without’ in ‘Inventory’:

Four be the things I am wiser to know:
Idleness, sorrow, a friend, and a foe.
Four be the things I’d been better without:
Love, curiosity, freckles, and doubt.
Three be the things I shall never attain:
Envy, content, and sufficient champagne.
Three be the things I shall have till I die:
Laughter and hope and a sock in the eye.

A rich, enjoyable puzzle.  Thanks you, Ifor!

Unfortnately, I have been unable to parse 20dn fully.
Thanks to Dave Hennings for the clarification.

Notation

(xxx) = definition
[xxx] = (anagram/homophone/container/etc.) indicator
XXX* = anagram
< = reversal
MAL = extra letter

Please post a comment if the explanations are not clear.