Changing fuel consumption of non-ion engines

yes, that one
lower numbers = less fuel used, and vice versa
@WiTriNo

@Zenithspeed Is it the massFlowRateOverride? It looks like it but I have no idea

for the procedural one then, simply change the mass flow to a low number
@WiTriNo

@Zenithspeed Sorry, I was referring to the procedural mage engine and thought there was a "fuel consumption" on the XML editor.

i can't tell if you're referring to the legacy mage engines or the procedural ones, either way here's my explanation for both:
legacy mage engine: this and also all of the other engines use the same system as the ion engine and thus can be configured to have zero fuel consumption
procedural engines: on these, the "mass flow" value shows the amount of fuel used, in kilograms/second, you can edit this to a low value such as 0.0001 (add as many zeroes after the decimal as you wish), however i don't reccommend setting it to 0 as it may cause bugs with the isp, while numbers on it above 0 are still mostly stable