I get it.

First case:

-You calculate the % dissociation as I have done in the original post.

-Then, for a base, % dissociation = x/[B ]_{0}*100 with x=[BH^{+}]=[OH^{-}]. If you know [B ]_{0} you can calculate [OH^{-}] the pOH and then pH.

Second case:

- Knowing [B ]_{0}, you do an ICE table, and solve for x=[BH^{+}]=[OH^{-}].

-Then you calculate % dissociation according to formula.

However, my question is still valid, at different temperatures, will the % dissociation be different?