One way: 
/A/g;
s/\G(.*?)A/$1a/g;

[download]
Another way: 
s{(?<=A)(.*)}{my $rest=$1; $rest=~tr/A/a/; $rest}e;

[download]
Without regex: 
substr($_, index($_, 'A')+1) =~ tr/A/a/;

[download]
And, combining techniques: 
/A/g;
substr($_, ++pos) =~ tr/A/a/;

[download]
Caution: Contents may have been coded under pressure.

In reply to Re: replace all but first by Roy Johnson
in thread replace all but first by texuser74

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