Main journals and rod journals just don't expand enough going from cold to hot to create much of a difference in oil clearance. So if your oil clearance is in spec when cold, it will be in spec when hot. So for a home mechanic freshening up an engine, that means that when all caps are torqued to spec, if the crank spins with the proper resistance when cold, it will still do so when hot.
Much more likely to be influenced by hot or cold is piston bore clearance. Pistons and to a lesser extent bores do indeed expand enough between cold and hot to create a high friction situation. At my buddy's machine shop, in the winter time when shop temperatures are lower and he is doing the final power hone on an engine block's cylinders, he will soak pistons in warm water before he measures them for their individual bores, thereby accounting for expansion and contraction.
Mike is of course correct when he states that if main caps are mixed up between two blocks, the solution (other than to "un-mix-up" them) is a trip to the machine shop for a line hone or line bore.
What other diagnosis have you done on this condition?
If the symptom is hard hot starting based on the starter motor having trouble turning over the engine when hot, well that could be a bad starter motor or bad wiring. What have you done to eliminate that possibility?
Have you taken any steps to measure the torque needed to spin the crank when cold vs how much is needed when hot? I would think that a torque wrench or spring scale applied to the crank pulley nut when cold vs when hot could help answer that question. You would take the plugs out to eliminate any compression-related variances, then start from a constant rotational position, say BDC, then pull the wrench and observe the dial or pointer or scale to measure, then repeat the process when hot. Of course this does not isolate the mains or rods as the pistons are still connected, but it would provide data that would absolve or condemn the starter.
It would be useful to use and endoscope or borescope to look thru the spark plug holes and at the bores for scuffing, which should be evident if the pistons have been fitted too tightly and are expanding when hot to the point where they are past the tight end of their fitment.