I think the one that most annoys me is the fact that they have changed "and tasting of his roseate Blood" to "and tasting of his precious Blood".
Now why do that?
The original in the Latin is
sed et cruorem roseum
gustando, Dei vivimus
Neale's translation renders that exactly, using "roseate" to translate "roseum". "Precious" is not there at all. And the phrase "precious blood" is too common and trite to be striking here. The image is, in any case, not meant to be one of price, but rather of the tasting of red wine. Sometimes these editors seem to be just crass.
The other less serious but apparently unnecessary piece of interference is in verse 4. This is what we have in the Latin:
Iam pascha nostrum Christus est,
agnus occisus innocens;
qui carnem suam obtulit.
In J. M. Neale's translation this went:
Now Christ, our Paschal Lamb, is slain,
the Lamb of God that knows no stain,
the true Oblation offered here,
our own unleavened Bread sincere.
The NEH editors have (in their wisdom) changed "paschal lamb" to "Passover". They have also changed round the last two lines, rendering them
And he, the true unleavened Bread,
Is truly our oblation made.
I don't think much of the rhyme (Bread and made), nor do I find the lines comprehensible in this approximation to English. Certainly these are no improvement on Neale's. In fact it looks to me as though sinceritatis azyma is a reference to the "unleavened bread of sincerity and truth" from 1 Corinthians 5.8.
So lines 3 and 4 ought to go "Sincerity's unleavened bread, who gave his very flesh instead."