add prechangegroup and pretxnchangegroup hooks. prechangegroup lets you stop push, pull or unbundle before it begins. pretxnchangegroup lets you inspect changegroup before transaction is committed, and roll back if you not like it.

#!/bin/sh

hg init rep
cd rep
mkdir dir
touch foo dir/bar
hg -v addremove
hg -v commit -m "add 1" -d "0 0"
cd dir/
touch ../foo_2 bar_2
hg -v addremove
hg -v commit -m "add 2" -d "0 0"