I assume that you are using pega password control feature and thru that you are enabling the passowrd expiry feature. In order to enable that you have to apply some changes on application level, browser requestor level and also in the web.xml files.
So I dont think it is possible to stop the password expiry feature for a specific set of users unless you associate them with a new access group and application having no relation to the password control specific ruleset.
I am not as familiar with 5.4, but if it operates like the current and recent releases, I believe that out of the box, password expiration policies are applied globally. If this is a feature that you would like to see, I would encourage you to file an enhancement request. This is a good time to file an enhancement request for this functionality because enhancing password expiry and account lockout functionality have been coming up a lot in the mesh in the past few months.