Can I Increase The Torque Without Increasing Horsepower?
You cannot have horsepower without torque, but you can have torque without horsepower! That's called a dump truck! Unless you want to just chug along on the shoulder, torque becomes a moot point for a daily application when it comes to performance gains on most folks bikes.
There is no replacement for displacement.
The most effective way to increase torque is to increase engine size, but since that's not really feasible or monetarily reasonable on many of Honda Shadows (unless you're trying to build a drag bike), your best bet is to increase HP which will bring the torque up.
The goal is maximizing engine output in the rpm range where the engine spends most of its time, whether it’s because of inherent design limitations,or because of intended use or a combination of these factors. This determines what upgrades you will make.
You can change the sprocket to a larger tooth count, which will make your takeoffs more zippy, but you will lose on the top end, that's the price ya pay. Conversely you can reduce sprocket size and then you lose on the bottom end, take offs are sluggish and your bike wont produce much torque until you are close to WOT in top gear.
The most simple means of increasing torque is to run an open exhaust and intake and tune properly. Torque value will increase right along with HP, so long as the tuning is performed properly. Aside from seriously drastic motor builds, these are the upgrades most people make to increase the overall performance of their motor.