Run bconf create limit=limit_name
For example, to create the limit X1 with a job limit of 23 per host:
bconf create limit=X1 "JOBS=23;PER_HOST=host12"
bconf: Request for limit <X1> accepted
Once accepted by bconf, the new limit appears in blimits output:
blimits -cn X1
Begin Limit
NAME = X1
PER_HOST = host12
JOBS = 23
End Limit