Use a look-ahead assertion. It looks ahead, but doesn't advance the position: 
  s/(^|\*)X(?=\*|$)/$1$NEW/g
#          ~~~

[download]
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re: global string replace by choroba
in thread global string replace by zX4hzjFWWT

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