writebyte(foo, svc_updatestat); //3
writebyte(foo, STAT_MONSTERS); //14
writelong(foo, statvalue); //byte if in qw. use svc_updatestatlong=38 if you want a long in quakeworld.
don't think you can hack nq's ammo values to show larger numbers by using this. ammo counts are duplicated in every. single. packet. to override them you would need to also send the info in every single packet. which is almost achievable, or rather it would be if you had a msg_unreliable_one.
as a result, this svc is only useful for monster/secret counts, and maybe csqc if you don't want to use the builtin created for the purpose.
-- begin engine code dump --
STAT_TOTALSECRETS = 11,
STAT_TOTALMONSTERS = 12,
STAT_SECRETS = 13, // bumped on client side by svc_foundsecret
STAT_MONSTERS = 14, // bumped by svc_killedmonster