Video format using LVDS signalling
Pin 2 selects either JEIDA data format or VESA data format.

So, I can select either 6 bit or 8 bit for the whole communication and
can't change in-between, right? So, I should go completely with 6-bits
or 8-bits with no changes?

You'll need to read the data sheet. You could always try it and see!

I can choose only one format for the data, right ? But not alternate
between both in-between ?

You'll need to read the data sheet.