After completing long_mris_slopes to get the rate of change and then concatenating them into one.mgh file for group analysis (mris_preproc). I am finally getting to mris_glmfit. Got a couple of questions along the way.

1). if I conducted long_mris_slopes, and got for example, lh.long.thickness-rate.fwhm10.fsaverage.mgh. Do I need to do a surface smoothing again (mri_surf2surf) before mris_glmfit?

2). I construct covariates in FSGD besides the group contrast that I am interested in. How do I add covariates into the glmfit model to control for the covariates as I contrast groups in terms of the rate of changing (CV vs. NCV groups) . Do I add them into --C as  (1, -1, 0(age), 0(gender), 0(race)).