Changing last entries in a comma delimited list

awk approach with sprintf function(to add leading zeros):

awk -F, -v OFS=',' '$8=sprintf("MI-%02d",$8);' file

The output:

36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-03
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-08
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-14
36,53,15596,0.58454577855,0.26119,2.24878677855,0.116147072052964,MI-12

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-F, - set comma , as field separator

$8 - points to the eighth field

%02d - format which treats function argument as 2-digit number

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Note, the last field in a record can be presented by $NF.

NF is a predefined variable whose value is the number of fields in the current record

So, $NF is the same as $8(for your input)

awk -F, -v OFS=',' '$(NF)=sprintf("MI-%02d", $(NF))' file

You can try using awk:

awk 'BEGIN { FS = OFS = "," } { $NF = sprintf("MI-%02d", $NF); } 1' file

Here's perl solution:

$ perl -F',' -lane '$last=$#F;$F[$last]=sprintf("MI-%02d",$F[$last]);print join ",", @F' input.txt                                       
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-03
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-08
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-14
36,53,15596,0.58454577855,0.26119,2.24878677855,0.116147072052964,MI-12

The -a flag allows us to treat input as array, based on separator specified with -F. Basically we alter last item in that array, and rebuild it via join command.