...
This is setup in the user_nl_cam namelist, using the following namelist variables:
(Note: An example is included in Notes on tuning 1 degree ACME v0 model)
interpolate_analysis = .true.,.true.,.true.,.true.,.true.,.true.
...
The interpolate_analysis options are for the different history tapes. It is a vector with 8 elements: seven different history files, plus inithist, which is the last one and should always be on the native grid.
In the code there appears to also be an option for the type of regridding (but I haven't tested it):
interp_type = 1 ! 0 = native high order, 1 = bilinear (default)
is included in Notes on tuning 1 degree ACME v0 model