Yes, this can be applied for crypto trading. There is some misunderstanding of the rule, usually. If you buy a coin without a stop loss (which is OK), then you risk 2%. If you open a position for 20% of your deposit and put a stop loss order on 10% this is the same rule. This doesn't mean that you use 2% of your capital, this means that you don't lose more than 2% on a trade