My take on this when initially developing our procedures for TS was that this would be included within our Engineering Change process, however following a discussion during a Training course with a representative of SMMT it was pointed out that although ECN can track all implemented changes, it does not necessarily capture any that are not implemented or which have a long implementation period (i.e. change not feasible or use up all existing stock, before implementation of change).
The guidance we received from SMMT was that there should be a process which logs the receipt of the specification, and logs the first response/review (this does not need to be anything more than an e-mail saying we have reviewed the specification and need x amount of weeks to fully assess the feasability). Therefore we simply have a log book and register where all specifications and responses are printed and assigned a log number which is available for review at audit.
However, during our latest TS survillance audit or auditor was of the opinion that the ECN process was sufficient and that he was not interested in changes which were not implemented, this is inspite of the fact that he had only been re-certified to audit TS by the very people who told me that the ECN system was insufficient

(SMMT). In summary it appears to me that the spirit of TS requires the process as recommended by SMMT, however the reality is that it is down to your auditors interpretation on the day