Question

from :help “A

“Vim fills these registers only when you say so. Specify them as lowercase
letters to replace their previous contents or as uppercase letters to append
to their previous contents“

Is there a way to turn this off?

it’s super annoying: when I hold down shift to type double quote ” to append to a register, its pretty often the case I hold the shift for a split second too long and input “A instead of “a (so it appends to register a instead of replacing it altogether)

Answer 1

If you wish to implement what @romainl has suggested it can be done in a six lines (three if you don’t mind having magic numbers, leaving unneeded variables and remapping in operator-pending mode):

let s:capshift=char2nr('A')-char2nr('a')
for s:ch in range(char2nr('A'), char2nr('B'))
    execute 'nnoremap "'.nr2char(s:ch).' "'.nr2char(s:ch-s:capshift)
    execute 'vnoremap "'.nr2char(s:ch).' "'.nr2char(s:ch-s:capshift)
endfor
unlet s:capshift s:ch

. But this solution has a drawback: you now loose ability to wait indefinitely between pressing " and A (unless you want to set notimeout which has problems on its own).