Dunno if this is of use at all... laugh

Your $chrs
33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 58 59 60 61 62 63 64 91 92 93 94 96 123 124 125 126
equal the octals
41 42 43 44 45 46 47 50 51 52 53 54 55 56 57 72 73 74 75 76 77 100 133 134 135 136 140 173 174 175 176

So you alternatively could use:
Code:
alias replaceIt2 { return $regsubex(repit,$1-,/[\41-\47\50-\57\72-\77\100\133-\136\140\173-\176]/g,_) }


But as $mknickfn() of your symbol string
Code:
!"#$%&'()*+,-./:<=>?@[\]^`{|}~
is:
Code:
_______()___-_________[_]^`{_}_
you'd only have to replace the remaining chars: ()-[]^`{}
For example:
Code:
alias replaceIt3 { return $regsubex(repit,$mknickfn($1-),/[\50\51\55\133\135\136\140\173\175]/g,_) }
which is the same as
Code:
alias replaceIt4 { return $regsubex(repit,$mknickfn($1-),/[()\-[\]^`{}]/g,_) }
(note that the "]" and "-" in the character class require escapes... that's why I prefered to work with octals)

However, $mknickfn() will replace additional chars, more than given in your alias. Only the "replaceIt2"-alias will exactly do the same as your - completely valid - $replace-approach.

Edit: like argv0 points out, it all depends on whether you want to replace a specific set of chars, or everything BUT a specific set of chars.