Hiya Silky,
If I understand you correctly, if you leave the "Climb Spd" blank in the CLB Perf on the ground, the FAC will compute green dot via the numbers entered in the init page. Once you are airborne, until slat retraction the FAC will use init page numbers and when the slats are retracted then the FAC will compute greed dot via the actual performance of the aircraft?
Cheers
P.S. Where in the FCOM can I find the commentary about the slat retraction.