Most, if not all, kindle haven't got the ~exec scripts left, so, unless you put them on manually that's only useful to a really, really low number of people (because you'd have to get a root shell in the first place to put them in, which means you wouldn't really need the ~exec command). (And the 3.0.3 update just killed them, btw ^^).
And, to answer your question, why try to do it this way, when you can already just hold [HOME] during a cold boot?
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