PS2: Are you thinking of actually having your change delay T3 as well?
With the tier 3 delay it would make it from 150 fuel to 165 fuel (note USF major is 170 fuel or 180 if gone captain)
I need to pull up OST and OKW tier 3 costs, but pretty much Brits still are cheaper in terms of there tier 3 cost. So it wouldn't delay it, it would put it in line.
Have I used mills bombs before? yes I have, MGs in garrisons are an example. Also just saying you can use nades in a defensive position.. I'm just giving an idea to make an ability that never gets upgraded actually used. Sappers don't need them imo.
With the UC carrier, in it's current forum may be an issue, however miragefla has a competitive mod where the repair ability is available straight away which works well. Plus you got to consider current brit meta of emplacement spam, how do we delay it without massive changes?