This patch will do it.  Of course we can just use:

(put 'replace 'scheme-indent-function 1)
(put 'add-after 'scheme-indent-function 2)
(put 'add-before 'scheme-indent-function 2)

But potentially these keywords may also be used outside 'modify-phases'.

So with the attached more complex rules, 'replace', 'add-before' and
'add-after' keywords will be indented specially only when they are
inside 'modify-phases', otherwise they will be indented as usual: