The only way to avoid that is to test on the same fabric as your pants before actually applying the heat n bond to your pants. Thinner or more loosely woven fabric are susceptible to bleed through. There's no fix that I know of, once you've applied the heat n bond, since the adhesive is heat activated and bonds extremely well to the fabric. Once it's saturated the fibers, it's there permanently.
However, sometimes wool fabric will turn shiny when ironed with a lot of pressure and without a cloth between the iron and the fabric, so if that's the case, that's fixable. To remove the shine in this case, you'll need a cloth (a white, clean dishtowel or pillowcase will do) that you'll place on the right side of the fabric, and make sure the iron is on the wool setting with steam. Hold the iron so it's very close to the press cloth, but not quite touching, and steam it. Be careful not to burn yourself. After steaming, while the fabric is still warm, use the press cloth to rub the shiny areas, to raise the fibers and reduce the shine. You can repeat this until the shine is gone.
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