To avoid getting into complicated issues like "at what point of the machine cycle the reload will happen" etc, would it not be a better idea to disable the timer interrupt when re-loading
or -even better- stop it. Why on earth worry about "Reload timer while it still running" when all it takes is clr TRn/setb TRn or TRn=0/Trn=1. Even easier to use a self-reloading configuration of the timer.

Erik