That sounds much much harder to pull off sensibly with INSS, especially since it breaks the communication of the bonus values and would be confusing to keep track of. You would have to do this instead with an INSS map where all bonuses (or at least all bonuses of one color) have the same number of territories, so players can figure out whether the bonus was -1'd or +1'd by just looking at the bonus link. On Biomes, they'd also have to count the territories.
Although you could also just change the bonus link to -1, 0, or +1 to indicate what had happened (and update the math for the sub-bonuses to still work out).
Alternatively, you could +1 or -1 at a color rather than bonus level, which would be easier to keep track of and you could just put in the game description.