That's already impressive, but why bother with chr in the first place? perl '-M0;@h{+a..z}=1'-pe 's/\d/(keys%h)[$&]/eg' input.txt works just as fine.

Edit: this can still be reduced a little: 

perl '-M0;@h{a..z}=1'-pe 's/\d/(%h)[$&*2]/eg' input.txt

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In reply to Re^2: A little golfing challenge: replace digits by random letters (updated) -- oneliner by Eily
in thread A little golfing challenge: replace digits by random letters by haukex

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