www.rallycrossuk.com has the following on the rule change:
"All Rallycross competitors are reminded that MSA Yearbook regulation G 7.11.1 has changed for 2005 and that the use of FIA homologated seat belts with (at least) four fixing points is mandatory."
As for your belts, I'm not 100%, if they're FIA approved but have 2005 expiration then I guess you should be ok for this season? Might want to double check that with an MSA official though before you turn up at scrutineering.