Correct overlaying TRANSACTION_CLASSIFICATION from RT::Record

I want to use different styles for Comment and Correspond in History.
As far as I can see ShowTransaction use data from %TRANSACTION_CLASSIFICATION as css classes.

Is this correct?
And how I can change


Create => ‘message’,
Correspond => ‘message’,
Comment => ‘message’,


to something like


Create => ‘message Create’,
Correspond => ‘message Correspond’,
Comment => ‘message Comment’,


Or should I overlay sub ClassifyTransaction instead?

Rather than modifying, you should use the callback in ShowTransaction:

    CallbackName => 'MassageTypeClass',
    Transaction  => $Transaction,
    TypeClassRef => \$type_class,
    ARGSRef      => \%ARGS,

So You have to put a file rt/local/html/Callbacks/YourOrg/Elements/ShowTransaction/MassageTypeClass with a content such as (untested):

if ( $Transaction && $Transaction->Type =~ m/^(Create|Comment|Correspond)$/ ) {
    $$TypeClassRef .= ' '.$Transaction->Type;

$Transaction =>undef
$TypeClassRef => undef

Thank You very much for this solution! Way better than overlaying.
I missed type_class in this callback.