This paragraph is a bit confusing I think.  Suggested rewording:

Another optional parameter, `flux_untruncated`, specifies whether the flux and half_light_radius should correspond to the untruncated profile or the truncated profile.  If `flux_untruncated` is True (and `trunc > 0` of course), then the profile will be identical to the version without truncation up to the truncation radius, at which point it drops to 0.  If `flux_untruncated` is False (the default), then the scale radius will be larger and the central peak will be higher than the untruncated profile, in order to maintain the correct provided `flux` and `half_light_radius`.