in reply to Repeated substitution on 1 side of a line only

No verbs needed. Just replace - with _, and once you find :, replace the whole remainder of the string with itself: 
perl -pe 'BEGIN { %h = qw( - _ ) } s/(-)|(:.*)/$h{$1}$2/g'

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Explanation: One of $h{$1} and $2 is always empty, as only one part of the alternative can match.

Update: Added the explanation and wrapped the hash initialization into a BEGIN.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

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Re^2: Repeated substitution on 1 side of a line only
by tybalt89 (Monsignor) on Dec 16, 2016 at 21:31 UTC

    Or skip the hash altogether... 

    #!/usr/bin/perl

# http://perlmonks.org/?node_id=1177915

use strict;
use warnings;

while(<DATA>)
  {
  s#-|(:.*)# $1 // '_' #ge;
  print;
  }

__DATA__
session-redis-hosts-fault-tolerant: "tyk-redis-1.gateways.svc.cluster.
+local,tyk-redis-2..."
message-center-db: "http://message-center-db-1b.message-center-db.svc.
+cluster.local"

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[reply]
[d/l]
      I wanted to get the result without /e or any other "advanced" tricks.

      ($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

      [download]
[reply]
[d/l]

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