Can you mix window grid patterns

Do you mean Different Patterned Glass in a Window ? Answer Yes if you like it.....

It depends. Look at the house from street view before deciding. Might look off balance or inconsistent. Mixing grid patterns on different sides of the house, yes.

Well can you and should you are two different things,you can do whatever makes you happy. Now if you mean that you put square those square things,sorry can't recall name, on some windows and diagonal in other ones if on front of home I personally wouldn't do it if you mean those types of windows in front and plain in back which no one notices then I say save money and do that it's very common to have basic plain windows on back of home. If you mean double hung and slider ones I wouldn't once again I personally would keep front one way and back plain but for instance my home is very basic traditional 80'style home front has those windows with front having those squares and back plain, it'snot bad except for dining room since it's L shaped so that you can see my dining room window when sitting in the living room and when we replace dining room window, depending on the price I may make it same as front. But like I said it's not that bad and I do have drapes so not much of the window itself is exposed,so I won't go into debt for it. Unfortunately for you I do like symmetry and I would keep front the same and sides and back depending on budget either the same as front or plain since it's what most people do.

Back in the '90's our town hired an architectural firm to survey all the houses in town that were over 50 years old and determine which of those had "architectural significance" I happened to read the descriptions of those chosen (our house was one of them) and it is really interesting how many have differences in the windows.

Usually grid patterns are kept consistent with the style of the architecture of the house/building. To mix them (see the second link with several kinds of grids) may make the house/building look chaotic. However, I have seen windows with a single row of diamond panes on top with square panes below. What style is the home/building you are wanting to put new windows in? One thing to remember, the more individual panes of glass, the bigger pain they are to keep clean!!