Yes, but you sacrifice a lot of phospor to get it. Constant-height screens are cool, but going that way with a 2.35:1 screen means setting up your raster with a 2.35:1 image in it (I believe not all CRT's can even squeeze this much). 1.78:1 has to be windowboxed inside that 2.35:1 image, so 1.78:1 gets shortchanged on both vertical and horizontal resolution as well as light output (kind of like 1.33:1 does with a 1.78:1 raster, compared to if you used your whole 1.33:1 tube face for it).
To get the same brightness at 1.78:1 as you have now (assuming the same size 1.78:1 screen) you'll have to run your tubes harder and that will shorten their useful life. Not to mention, depending on your particular projector, you could lose a lot of detail esp. with HD material (or not if you have a 9" em focus machine).
I know some people do 2.35:1 constant-height anyway, but it is not for me.