If you want to create a reseller manually in the database you will have to add records to the tables: isp_nodes, isp_isp_reseller, sys_nodes and sys_user.
For a client records has to be added to the tables isp_nodes, isp_dep, isp_isp_kunde, sys_nodes and sys_user.
If the records have to be written to config files (like isp_isp_web, isp_isp_user) there is a field "status" that has to be set to "n" for new records and "u" for updated records.
There is an extension to add Resellers, Clients webs, Co-Domains, DNS-Records etc. with SOAP remote calls from external applications for 42goISP.