As the Dominion I'm all for enhancing my Intelligence capabilities
. However let's look at the sort of work they did. excuse me if i forget some.
1. Impersonated an ambassador so that DS9 nearly started a war with the Tzenkethi. Diplomatic intercept?
2. Impersonated a Romulan captain to lead the Tal'Shiar and Obsidian order into a trap. Information gathering?
3. It wasn't their plan, but they impersonated Chief O'Brian so that Sisko knew about a Federation rebellion. This wasn't really any sort of attack.
It would seem to be limited to actions that are minor but have a farreaching impact. They couldn't change crew rosters because the rest of the government would notice and fix it, but putting target ships off course, or even a whole fleet for a turn, seems in character. It has to be something that raises no questions. so obviously no mutinies as the loyal crew is going to suspect their captain wanting to change sides, and obviouslly they can't steal whole planets, although they can gather information on ship and planet cargo. Bombs also fit.