you can restrict killstreaks in in the tdm.cfg file (and I assume other gamemode specific cfg files)
using the following
restrict_item "killstreak_spyplane" // UAV restrict_item "killstreak_rcbomb" // RC-XD restrict_item "killstreak_missile_drone" // Hunter Killer restrict_item "killstreak_supply_drop" // Care Package restrict_item "killstreak_counteruav" // Counter-UAV restrict_item "killstreak_microwave_turret" // Guardian restrict_item "killstreak_remote_missile" // Hellstorm Missile restrict_item "killstreak_planemortar" // Lightning Strike restrict_item "killstreak_auto_turret" // Sentry Gun restrict_item "killstreak_minigun" // Death Machine restrict_item "killstreak_m32" // War Machine restrict_item "killstreak_qrdrone" // Dragonfire restrict_item "killstreak_ai_tank_drop" // A.G.R. restrict_item "killstreak_helicopter_comlink" // Stealth Chopper restrict_item "killstreak_spyplane_direction" // Orbital VSAT restrict_item "killstreak_helicopter_guard" // Escort Drone restrict_item "killstreak_emp" // EMP Systems restrict_item "killstreak_straferun" // Warthog restrict_item "killstreak_remote_mortar" // Lodestar restrict_item "killstreak_helicopter_player_gunner" // VTOL Warship restrict_item "killstreak_dogs" // K9 Unit restrict_item "killstreak_missile_swarm" // Swarmthis will just disable the specified killstreak. I am currently not aware of a way to replace a killstreak with a different killstreak. I'm also not sure if a restricted killstreak can still come out of a care package