It is certainly possible. Assuming Windows command line (update: and assuming "black" means "blank"), try (semi-tested): 

perl -wMstrict -pe "BEGIN { our $armed } $::armed = /\A \\macroa \s/x 
+? 1 : /\A \\macrob \s/x && $::armed && ! print qq{\n}" infile > outfi
+le

[download]

Give a man a fish:  <%-{-{-{-<

In reply to Re: Add black line between two consecutive lines starting with specified strings by AnomalousMonk
in thread Add blank line between two consecutive lines starting with specified strings by texuser

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