If you put on an MTB crank you would be able to shift between two of the chainrings but not all three. You'd have to choose between the inner and the middle or the middle and the big.
The gear inches for 22, 24, and 26 tooth chainrings on the 34 tooth rear cog are 17.5, 19.1, and 20.6.
In my opinion it's not worth making any changes.