Try the following tagger script and see if it does what you want.
$setmulti(releasetype,$map(%releasetype%,
$if($eq(%_loop_value%,ep),EP,
$if($eq(%_loop_value%,audio drama),Audio drama,
$if($eq(%_loop_value%,dj-mix),DJ-mix,
$if($eq(%_loop_value%,mixtape/street),Mixtape/Street,
$if($eq(%_loop_value%,field recording),Field recording,
$title(%_loop_value%))))))))