I replaced the rotor bearings (and since greased them more often with a not worn out grease gun fitting) while doing the "rotor flow kit". The flow kit may help but I didn't find it worth the money. If you do the flow kit, you end up replacing the front metal that the bearings are supported by. The kit comes with a little "stand" to support the front of the rotor up. I used it, but a few blocks of wood would shim the rotor up just as well. You should be able to do the process through the grain tank. Having said that, if the rotors need worked on such as new teeth, pull them out the back. If the impeller needs worked on, pull it. Pulling either the rotors or the impeller will make the job nicer, but both can be left in place. If your rotor intake strips (elephant ears) are pretty worn, they should be replaced at this time a well, and can be done from the tank, but it would be much easier to pull the rotors also.
For repairing bearings through the grain tank, I am not very confident how to do so, because I did the flow kit at the same time, and I am unsure what does and doesn't need removed. The bearings hold the rotors from sliding forward. Take a ratchet strap and hook it on a rotor tooth near the back. Run the strap back and around to the other rotor and tighten so they can't slide forward. I think you need to remove the entire front section of sheet metal that supports the bearing, to replace the bearing. The puller I made was used from one of the front bearing plates. This is the item just behind the impeller where the grease comes out. I drilled a hole in the very center of it and threaded the hole with maybe a 1/2" bolt. When ready to pull the bearing, I used this puller and by tightening the center bolt through the new hole, it pulled the bearing forward. You first must remove this cap, and pull out the factory bolt in the middle of the bearing that holds the bearing onto the rotor. When using the puller, the hole behind the middle of the puller cap needs filled with a bolt without a washer so the puller doesn't damage the threads. This newly threaded hole on the "cap" will need a very short bolt re-installed upon final assembly to keep grease in and dirt out.
The first two pics show what it looks like with the impeller pulled. You would still do the majority of the work from within the tank, but would have much more room. The pics shown have the factory, old style bearing holder. The rotor flow kit comes in black instead of grey and doesn't angle upward in the middle of the machine. The third pic shows the original bearing holder removed from doing the flow kit (with impeller installed). It also shows the rotor block to hold the rotor up, as well as the four small elephant ears. These elephant ears are each held on by three allen bolts and nuts. The mounting holes are slotted and it was recommended to me to install the ears forward as far as possible without striking the back of the bearing plate. Too much gap and material could possibly wrap around the front of the rotor. Notice the anti-wrap keystock in the back of this picture on the second bearing holder. This was likely the most difficult part...adjusting the ears without hitting, and then getting them tight with the impeller in my way. It was accomplished, but difficult. The fourth pic shows the "cap" that I used as a puller. I drilled and tapped a hole in the middle of it. With the two factory bolts installed and the tapped hole with bolt in the middle, it will pull the bearing assembly forward, off of the rotor. Don't forget to use the upper two grain tank access holes if needed. Don't cross-thread the two grease fitting lines while re-assembling.