Is this one of those circuline bulbs with the ballast in the middle and a bracket that mounts to the ballast and holds the bulb?
these bulbs were used extensively in the hotel industry before cfls came out or better put old technology.
Yes you can switch to a different kelvin bulb without a problem.
But since you are fruggel you are going to be shocked at the prices. You will be able to find them at electrical / lighting supply stores (Rexel / Branch electric) but the last time I checked they were $12.50 each, you can get 6 cfl's for that price at walmart.