You can make it fancier by storing function references:

my $action = \&initial_action;
for (@input){
    if (/$Start/){
        $action = \&do_this;
    } elsif (/$Finish/){
        $action = \&do_that;
    }

    # perform your action
    $action->(); 
}
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But it might depend on your idea of "simple" if that's really more simple.