If, in the Bank's credit card agreement document, there is a statement such as...."the periodic rate is subject to being increased to a permanent rate of 18% per annum if the account is not maintained in good standing," must this rate be disclosed on the Reg Z application disclosure?

IMO yes. I would consider this a "default rate".

Actually the commentary to that cite (226.5a(b)(1)(7)) is what I'm basing my opinion on. You are going to increase the rate if the account is not maintained in a satisfactory manner, therefore I consider that a penalty/default rate. The increase will take affect based on some specific event that will cause you to no longer deem the account in good standing.