It is of the greatest importance to know what you mean when referring to "derate".
Current thinking is that derate is selecting a new, lower, thrust limit for the engines and may just cover this take off or this flight or always - think airways/landing fees and whether you need the extra performance or TOW - and engine costs may be tied to derated thrust on so many occasions. Reduced thrust is the other option, maybe assumed temperature, which leaves the limit thrust unchanged and hence Vmca is for full thrust.
When using derate, all speeds are calculated using the new, lower, thrust as the baseline, hence a throttle push can raise Vmca potentially above your current speed.
Be very careful if you want to push up the thrust, remember that certified performance will be met when using derated figures, so why mess with it?