[Varyon]

Replacing reaction mass with something else that gets used up (typically some sort of energy-producing fuel, but coolant could be an option) can be interesting from a background standpoint, but typically doesn't have a lot of impact on how ships function in the setting (aside from letting you ignore the issue of dangerous exhaust). Coolant can be a particularly interesting variant, because one can (presumably) use it a few different ways. A vessel with resupply readily available nearby can keep itself comfortably cool by venting coolant (probably using heat pumps to shunt heat into a small portion of it, boiling it, then releasing the steam). One that needs to be more conservative is going to tend to get rather warm during engagements and the like, as the coolant keeping the thrusters, power plants, and weapons from melting has no choice but to evenly distribute all that heat throughout the ship, radiating what little heat it can into the vacuum of space passively. In a crisis situation, the captain may have to make the difficult choice between venting coolant to keep important components (like the crew) from overheating or having enough available to be able to get back home in a reliable timeframe (or just have enough to get through the next battle). It may also influence tactics and decision-making from the other side ("Captain, their ship appears to be out of coolant. If we keep pursuing them, they're going to have a complete meltdown of their thrusters; the resulting antimatter explosion will almost certainly kill their hostages.").

What replacing reaction mass with coolant doesn't get you, however, is a useful spaceship that cannot be used as a WMD. For that, you've more-or-less got to break physics - teleportation, pseudovelocity, hyperspace travel, etc. Heck, even those still get you WMD's in the form of orbital drops, so you've got to combine them with the sort of social structures that prevent that.