I think he means changing the final drive gearing; the bigger wheel being a bigger driven gear. Where you'd even get that I have no clue unless you could use a whole transaxle from a different year RAV4 but then you'd also have to change the rear differential.I'm not sure to understand exactly what you want to do. What do you means by ''bigger wheel'' and ''small shafts''... can you explain it with different words please?
Way back when we had that option with the underpowered 70HP Tercel 4WD wagon since Toyota changed ratios midway thru the production run.
IMO, altho the intention is on track the implementation is FAR more complicated than the idea.
The practical solution: Buy the Suzuki!