The setting hard at room temp is no issue.
We preheat the stored fat, then that liquidises and moves to another heated tank.
Then there is a preheater before the injector pump.
I would envisage starting on diesel, running on the heated fat, and running down on diesel (With one of my modified turbo timers)
Ive been converting cars to run on veg oil for almost 9 years now - and Ive been through a good few different systems getting them right
Its simple enough to get round the common rail issues - theres not much that cant be solved with a good lift pump