For the B747-400:

The control wheel trim switches must be moved together. This signals both trim control modules, through the Normal electrical channels, to position the stab with both trim actuators.

Autopilot trim uses the same normal electrical channels as control wheel trim. However, the autopilot can only use one channel, the left or right depending on autopilot selected. This is why the autopilot trims at "1/2 rate".

Since both control wheel trim switches and autopilot trim use the same electrical channels, if the autopilot is engaged and the control wheel switches are actuated, the autopilot disengages. If multiple autopilots are engaged, then control wheel trim is inhibited.

What you are referring to are the Alternate Trim switches.

The Alternate Stabilizer Trim switches provide trim commands in the same manner as the Stabilizer Trim switches through separate control channels.

They provide increased trim range and since ALTN Trim uses a separate control channel, it will override autopilot trim regardless of which autopilot(s) are engaged.

The ALTN trim will not disengage the autopilot.