Yes, you absolutely can; most can be double more or less safely, but if there is a true excess, it could probably cause excessive slime coat, decreased water oxygen, gill trouble, etc.
What conditioner do you use, and what is the reccomended dosage? I use Aquasafe; it is 1 tsp per 10 gallons. So, my 5 gallon tanks get 1/2 tsp, my 2.5 gallon tanks get 1/4 tsp, and 1 gallons get 8-10 drops (recomended on the mini-size). I would say that so long as you approrpiately adjust your dechlorinator, it should be fine.
