Using spamassassin 3.0.0 on my ISP whatever I set the score to in my rule set, when the event is triggered the score is always 1. I am using the following as a test
add_header all tf Score Values (_TESTSSCORES(,)_)
rawbody TF_RAWBODY_WARNING_1 /message\.scr/i score TF_RAWBODY_WARNING_1 20
As spamassassin is running on my ISP I can not give very many details about the setup, they have been unable to answer this question and I have been unable to find the answer either!
Does your ISP use spamd? (most large sites do).
If so, did they (foolishly) set allow_user_rules to 1?
If not, any rules in user_prefs should be ignored. The fact that your rule is even executed is a security hole.