I heard some rumors about Tseng Labs chipsets allowing to use higher refresh rates in standard VGA modes...
I've got an ET4000/W32i card, along with the dedicated software (notably SETCRT.EXE), so I did some experiments...
But no, I can't change the refresh rate for text modes, nor low-res graphics modes.
I can change rates for 640x480 and higher, including standard VGA modes 640x480x2 and 640x480x16 - to up to 90 Hz.