ma’am does an auditing firm needs to mention in the engagement letter its use of auditor’s/management’s expert? and does the engagement letter needs to be reissued if the auditor’s/management’s expert is hired/changed in the midst of the audit?
ISA 210 says “when relevant”, the engagement letter COULD (so not must) refer to arrangements concerning the involvement of other auditors (i.e. in group scenario) and “experts” – it doesn’t specify whether management or auditor expert. Any mention would be in general terms (would not name individuals) so certainly no need to reissue an engagement letter in the event of change. Unless something is a matter that affects the TERMS of the engagement there would be no need to change “mid-audit”.