Cyclone IV EP4CE75F29I7N

What do you mean by 'circuit level equivalent'? That you can reuse the EXACT same programming/configuration files without recompiling?

If so, that part will NOT work, it has a different number of cells and a thus a different configuration file is required.

You can change speed grades / environment class (the trailing xI7N) from industrial (I) to commercial (C) or the speed grade (4,5,6,7,8,9 etc) without doing a recompile, as the same programming file is used. However, that being said, depending on the timing optimization or usage of the part it may or may not work in circuit (ie, if you really need I-class temp range to function a C-class part may not meet timing).