Thanks :), I've always loved to play with them. You can do all sorts of things, really sparkles my imagination. I hope they work the same in CSS, I've never tried to be honest.
Well, if you want to disable all or just one killstreak after one has dropped you could simply disable it's timer which controlls the random drops until you want it to be availble again. This can be done easily with anything from a simple logic_relay to another secondary timer, which are activated once one killstreak (or one logic_timer that is controlling a killstreak) has been fired.
Using a secondary timer would be to make it overly complicated though, I'd choose a logic_relay. You'd simply activate the relay along with the killstreak, the relay would have two outputs, one that disables the timer directly, and one that enables it again once a given time has passed.