split_sreg_range

Set value of a segment register.
     ea - linear address
     reg - name of a register, like "cs", "ds", "es", etc.
     value - new value of the segment register.
     tag   - one of SR_... constants
IDA keeps tracks of all the points where segment registers change their
values. This function allows you to specify the correct value of a segment
register if IDA is not able to find the correct value.

success split_sreg_range(long ea, string reg, long value, long tag=SR_user);

#define SR_inherit      1               // the value is inherited from the previous range
#define SR_user         2               // the value is specified by the user
#define SR_auto         3               // the value is determined by IDA
#define SR_autostart    4               // used as SR_auto for segment starting address