Permutating keys at bitlevel good idea?

Could it be a good idea working with bitpermutation at key?
When rescheduling key?
I know how to do it at low cost but is it a good idea, what is the
optimal bytelength before rescheduling key, if we play with the thought
that it is used for a cipher with the heart in a 256 byte permutation.

I understand that distributions of 0 and 1 will render different many
unique solutions if used strictly with permutation so maybe a XOR of
password during keysetup would be beneficial


JT

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