The extra weight that screws on at the back of the tonearm does not increase tracking force, on the contrary, using it would decrease tracking force. The extra weight is used together with really heavy cartridges, like the Ortofon SPU series. On the other hand I would probably question a persons sanity if they used that kind of cartridge on an original Technics 1200 tonearm.
What you want to use with a DJ cartridge to get the correct tracking force is the extra weight plate that is placed between the cartridge and the headshell. Of course this is not valid when using a Concorde type of cartridge. With these you should be able to get the right tracking force as is.