The only way you can do it is if you unlink it. You cannot modify the source tracks of a digitised clip.
I've tried a thousand and one different things to get the Avid to 'see' tracks 1&2 as tracks 3&4, but it won't. I don't have access to MC or Symphony (although I'm able to log a 4-track masterclip in AXP anyway) but I'm pretty sure this won't work. This poses a problem when you use decks such as the J-H3 which can output a maximum of 2 tracks at a time. I'm working in 4.8.1 so maybe things are different on later system but as far as I can tell, there's no way to create a 4-track source clip from 2 x 2-track clips. But, of course, Avid only allows you to make 2-track mixdowns. My original thinking was to make some sort of 4-track mixdown. Again there appears to be no way of creating a 4-track source clip (where a group, subclip or master clip) when you start with 2-track sources. If, following the 2nd method, I create a 4-track sequence, select it and chose autosync, all I get is a new subclip with, at best, 2 tracks of audio. No 4-track clip can be made via this method, as far as I can tell. If I export on OMF of a 4-track sequence and then re-import it back in, all I get is the same separate 2-track clips I had originally. Maybe I'm being daft but I cannot get either of these methods to work.