I highly doubt you can 'unlock them through the gamesave'. it says here that

By starting private matches and inputting a number of console commands, players are supposedly able to turn on a “Global Thermonuclear War” mode, an objective-based gametype that has players scrambling to capture – and detonate – a nuke placed somewhere on the map. Assassination/VIP-escort modes and variations on capture the flag were also allegedly unlocked and tested.

Since we PS3 users can not input console commands like you can on PC, it seems to me like we wont be able to unlock them. and it says that you need to start a private match to do it, so even if someone did figure it out on PS3, you wouldnt earn XP. it would however be a fun twist when the game gets boring.