Just add less water, and get it stronger that way. Ten percent less water, 10 percent more sugar, and it will be stronger but not very different.
Don't add own pears now, just try it as the instructions say.
You COULD however set some liquor aside, juice pears and add them in a separate vessel. So you would have two vessels: one original, and one you screwed around with. Oh, and extra yeast perhaps.