How about using autosplit mode? 
perl -F, -lape'join(",",@F[0..3],$F[3],$F[4],@F[4..$#F])' data.txt

[download]
I like to start out with something like: 
perl -F, -MData::Dumper -lape'Dumper \@F' data.txt

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To make sure that i am populating @F correctly first, then move on. Once you feel comfortable, you can add inplace editting: 
perl -F, -lapi.bak -e'$_=join(",",@F[0..3],$F[3],$F[4],@F[4..$#F])' da
+ta.txt

[download]

UPDATE:
replaced -lane with -lape and dropped print ... silly /me ;)

UPDATE2:
fixed error pointed out by nr0mx and duff ... thanks guys :)

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

In reply to Re: Need help constructing a one-liner by jeffa
in thread Need help constructing a one-liner by nr0mx

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