Depending on the structure of your code, you could use somehting as simple as localizing STDOUT.

print "Msg to original STDOUT\n";
{
   local *STDOUT;
   open(STDOUT, ">my_file") ;
   select STDOUT; $| = 1; 
   print "msg to Redirected STDOUT\n";
}
print "Msg to original STDOUT again\n";
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Note that the localized copy of STDOUT will be used by any subs called from within the block (after the local), unlike with "my", but from your post, I think that's what you want. (Localizing STDOUT when you change it is good practice in any case.)