Do you mean to backup the whole directory? Or just your profile? I'm going to assume you mean your profile.
Navigate to <your SPT-AKI folder>/user/profiles and copy the json file of the profile you'd like to make a backup of. Then simply paste that copy somewhere you won't lose it. Probably not within the SPT-AKI directory itself so you don't accidentally delete it when upgrading to a new version.
now with my profile backed up, if i mod i should be fine? or should i back up my game instead?