In black-and-white film, processing is the normal way to attain this. There is no real way to do it with filtration - some filters might cut down contrast incidentally, but will have other effects.
You can do zone-system-type processing effects on rollfilm. The easiest way is to do it on a 120 camera with interchangeable backs. Dedicate a back to a specific type of exposure, and change the back if you want to compress or expand contrast. Another option with 35mm film is to use multiple bodies - which in this day and age is easier than it was in the heyday of film. At the time of writing, you can get some reasonable low-end film SLR cameras for under $20 US. (For some types of photography, like landscape photography, the features of the camera are going to be very secondary to the lens choice.)
You can adjust shadow contrast through flare effects, though. For example, using an uncoated or single-coated lens instead of a multi-coated one will result in more detail in the shadows and less contrast. The degree of this will depend on the amount of light that is being reflected off the elements, so strong side light or back light may be necessary to make a strong effect. You can probably simulate this effect through the use of a filter (perhaps a very dusty one, or some uncoated filters stacked in front of the lens) but you will probably lose some resolution in the bargain.