The pipe character (|) means alternation inside a regex. It needs to be escaped. Try s/\Q$rem\E/$rep/g.

---
print map { my ($m)=1<<hex($_)&11?' ':'';
$m.=substr('AHJPacehklnorstu',hex($_),1) }
split //,'2fde0abe76c36c914586c';
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