Using dvar to change number of max attachments

Im trying to use the following dvar:
0x83754CB0 - Type: DWORD - maxAttachmentsPerWeapon
Max attachments allowed for a weapon
to increase the number of attachments i can use in create-a-class. I tried doing /developer 1, followed by sv_cheats 1 and then maxAttachmentsPerWeapon 3, but nothing happened. This was in combat training. Do i need to host a private server with bots to use it? What do I need to do?