Would the discovery of a second APN # on a parcel of property (which then incurs an additional Tax Service Fee) be considered a "changed circumstance" such that we can reset tolerance with a revised LE and charge the additional fee (a zero tolerance fee)?

If you couldn't have previously known there was two - sure. If it was an oversight - no.

19(e)(3)(iv)(A)(3) New information specific to the consumer or transaction that the creditor did not rely on when providing the original disclosures required under paragraph (e)(1)(i) of this section.