Hello!
To expand the size of the inventory you need to edit this file: Core.cpk\Scripts\Characters\State\PlayerCharacterPrivateState.cs
find the line with "slotsCount: 40" and change it as you want. The change will be applied to new characters on this server (this is only a server-side mod, client-side changes will have no effect).
Please note that the inventory after this change will have a scrollbar and it's not as convenient to use.
Regards!