Have you thought about doing this with a slice?

my $str = "jigglewort";
my @a = split //, $str;
print join('',@a[0..$_-1, $_+1, $_, $_+2..$#a]),"\n" for 0..$#a;
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And the output is as expected -

ijgglewort
jgiglewort
jigglewort
jiglgewort
jiggelwort
jigglweort
jiggleowrt
jigglewrot
jigglewotr
jigglewort
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