I didn't think this was even possible, but I did it:
~/cmdstan/stan/lib/stan_math(develop)$ git commit -a -m "refactor, doc, replace const T with const T&"
[develop 4d7a8f2] refactor, doc, replace const T with const T&
29 files changed, 215 insertions(+), 277 deletions(-)
rewrite stan/math/prim/mat/err/check_ldlt_factor.hpp (67%)
rewrite stan/math/prim/mat/fun/rank.hpp (76%)
~/cmdstan/stan/lib/stan_math(develop)$ git push
Counting objects: 85, done.
Delta compression using up to 8 threads.
Compressing objects: 100% (47/47), done.
Writing objects: 100% (47/47), 10.27 KiB, done.
Total 47 (delta 32), reused 0 (delta 0)
remote: Resolving deltas: 100% (32/32), completed with 30 local objects.
6f02a99..4d7a8f2 develop -> develop
Now the question is how to I undo that magic?