it will only crack if you hit it too hard. the bats not just going to crack because youve hit it once more than it needs.
I had heard that Tim at NEwbery used to knock in the bats in a similar way.......I have knocked in a bat like that, but with a slightly bigger hammer and it works if done carefully. Took me 30 minutes to knock-in the bat and it played really well.Only con is that you may get some very circular marks, but these can be made to disappear by rubbing the bat against the round edge on a bath tub or a ceramic wash basin......
Can I see a pic of your bat please? Because I might use this technique, but I'm a bit skeptical.
best using a cobblers hammer as it a rounded head, bit dodgy using a flat headed hammer but then again if sehwag cracks it,it doesn't really matter to him