A variation using substitution can do some input validation as well (tested):

s{ \A (\S+) \s+ (\S+) \z }{@{[ $2 eq 'WR' ? 'wire' : 'reg' ]} $1}xms
    or die "bad input: '$_'"
    for @lines;
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(The messy stuff in the  @{[ ... ]} should probably be factored out to a subroutine.)