It wasn't that hard. My code was wrong. If you look at system var you will see that it's a VECTOR.
QuoteDisplay MorePROGRAM Probata
VAR
ent1 : INTEGER
status : INTEGER
VECTORa : VECTOR
BEGIN
VECTORa.X = 2.4
VECTORa.Y = 3.5
VECTORa.Z = 10.4
SET_VAR(ent1, '*SYSTEM*','$XSP_SCH[1].$SENSOR[1].$TRACK.$CORE.$BIAS.$VECTOR',VECTORa,status);
END Probata
I still have no answer from local support.