It's possible that it might but it depends on the specifics of what you have done. Not sure why you would break it out into two steps, what were the conditions at each step? By grinding in between it might affect some surface area and a few other things but hard to say without just going ahead and characterizing the biochar.

Yes, pyrolysis can be done in two steps instead of one. This approach is often referred to as “two-step pyrolysis” or “catalytic pyrolysis.” In the first step, the biomass or organic material is heated in laboratory devices (special ovens) in order to break down the large molecules into smaller granules, resulting in bio-oil and char. Further heating or catalytic treatment of the bio-oil is carried out to improve the yield or quality of the product.

The temperature must be regular because it has a significant effect on the material to be heated inside the oven, which leads to improved efficiency and product properties. It can also facilitate the use of specific catalysts that may be more effective under certain conditions.