Probably a question best left for Yaobing, but;
I know you can set a preference for a particular tuner by channel in "Manage Channels", but I don't think that forces MC to use that tuner. If the tuner isn't available, MC will try to use another tuner.
Also, if MC is forced to use another tuner, I believe that it will try to use a tuner from the same "Tuner Profile". So if the Ceton and SD tuners are in different Tuner Profiles, then your requirement would be met. But I think Tuner Profiles need to be defined by the tuner type, i.e. ATSC, Card Card, DVB-T, etc., rather than the brand, so setting up separate profiles may cause issues.
I know Yaobing has said before that there should be only one profile, for example, for ATSC tuners. However, there was some discussion around grouping, similar to your question.