The above comments gave a kinda brief explanation about it, however, if you wanna get more 'in-depth' about it, this could either be done from the database (where you could do everything related to a server) or from the SMC like the above comment stated, if you wanna do it through the database, first lemme give you a brief explanation about the Security Groups in sro, the sro security groups start from number 1 to number 7 by default (if no custom groups were made), descending from server developer (the most powerful security group) at sec_content of 1 and going down all the way to 'Content GM Leader' at the sec_content of 7, this image actually shows what i was talking about and it could be found at the _SecurityDescription table of the account database :
moving up to what is the privileges of each of the security groups, that's where we need a "privilege" to assign, and this can be easily found in the _SecurityDescriptionGroup in the account database, usually there are 34 privileges, starting from ID 1 to 34, where you can literally control what the account can do, from SMC activities *viewing some functions and not the others* all the way to ingame privileges, this picture should provide some visual aid to ya regarding this :
and now, to assign these privileges to each category of the security groups, you need to just head to the _SecurityDescriptionGroupAssign table in your account db, there you'll find 2 columns, one with the groupID and one with the description (or the privilege) ID, where you insert the number of the group you wanna edit, insert what privileges you want this group to just have, and that's it, and to disable ingame item creation, just assign SR_GM_Lvl1 and SR_GM_Lvl2 i guess (not sure about that though cuz i forgot which is which, but the above comment said SR_GM_Lvl2 was enough so its okay), however, you should have a background knowledge of the situation now. Good luck, and last but not least, here's a screen of the assign table :
good luck.