Don't allow --style and --template for hg update and hg merge. The only way that changesets will be shown with these command is in an error message when trying to update to an ambiguous branch name.

#!/bin/sh

hg init a
echo a > a/a
hg --cwd a ci -A -m a
hg clone a b
echo b > b/b
hg --cwd b ci -A -m b
chmod 100 a/.hg
hg --cwd b push ../a
chmod 700 a/.hg