Passphrases, Dictionary attacks and 'bit shift' How much better would a passphrase be if you swapped the first letters of each word with a shift to the left:

"correct battery horse staple" becomes "borrect hattery sorse ctaple"

This would be simple to remember because you know all the  words but how much harder would this be for an attacker? 

Further, we could try this with the first and last letters of each word producing:
"torrecb yatterh eorss etaplc"
(This at least reduces the chances that swapping the first letters will still result in normal English words, like 'hattery' in the first example)

How much harder would this make it to crack, is it worth the extra effort to remember?
Do dictionary attacks consider things like this?
If you ask a computer to pick a sequence of four words out of 10 000 (with replacement) uniformly at random, there are about $2^{53}$ possibilities; an attacker can expect to guess $2^{52}$ of them before getting the right one.  (For scale comparison, the Bitcoin network guesses and tries thousands of times more possible inputs than that to a hash every second.)

If you ask a computer to pick a sequence of four words out of 10 000, and one of the 24 permutations of four elements from the symmetric group $S_4$, then there are about $2^{53} * 24 \approx 2^{57}$ possibilities, although the number of distinct outcomes will dwindle once you account for alliteration.

If you ask a computer to pick a sequence of five words out of 10 000, there are $2^{66}$ possibilities, all distinct.

Which would you rather memorize: a permutation in $S_4$ causing words to be spelled differently, or another word?  I'd take the other word—in fact, I'd take six other words and invent a mnemonic for myself, to raise the number of possibilities above $2^{128}$ so an attacker has no hope of ever trying anywhere near enough passwords to guess correctly even in an offline parallel attack.

But whatever you do, don't try to pick the words and permutations yourself in your head.  Your mind is a terrible source of entropy.