Well, we know for sure that these devices are called "Bussard collectors" and that they can spit out hydrogen. But that's basically all we know of them. We don't even have confirmation that spitting out hydrogen means a reverse mode of operations. For all we know, it is the normal mode instead.
For all we know, Rebecca Bussard in the Trek universe invented a way to collect waste gas from magnetically contained plasma and then harmlessly exhaust it without losing plasma containment in the process, greatly increasing the efficiency of things like fusion reactors and, later on, warp engines. This is why the Bussard collectors must be next to the warp nacelles from which the hydrogen is collected. But not every engine uses a turbocharger, and Klingons might have other ways of boosting their warp engine performance.
Timo Saloniemi