for the razor rules you need this
score 5.0 RAZOR2_CF_RANGE_51_100
score 5.0 RAZOR2_CF_RANGE_E4_51_100
score 5.0 RAZOR2_CHECK
And yes, if you read the spamassassin documentation as well as the wiki, writing of rules is explained. You can also look at the rules that come with the installation. You will be some basic perl knowledge though to understand them.