To change the identity gap for a specific table, use sp_chgattribute:
sp_chgattribute "table_name", "identity_gap", set_number
For example:
sp_chgattribute "mytable", "identity_gap", 20
To change mytable to use the identity burning set factor setting instead of the identity_gap setting, set identity_gap to 0:
sp_chgattribute "mytable", "identity_gap", 0
See the Reference Manual: Procedures.
