I read it as follows:
In 420, col.2 for
"Charles Henry" read
"Charles otherwise Charles
Henry" & col.3 for
"30" read "36"
From that I think we could infer that he was officially just Charles (or his birth was registered as that) but for some reason he was known as Charles Henry. I've just looked at the full entry (at Ancestry) and I see it was amended on the basis of a statutory declaration; I suspect it might be something like clearing up an apparent discrepancy with his service records. The vicar's name in the margin doesn't match the vicars shown in the register in 1916 (there seems to have been a change), so it could have been done some years later.