Instructor Rating
Correct me if I am wrong - my understanding is that under the new Part 61 there is no need to go through an initial flight test to renew an MECIR even after a prolonged period of expiry but in the meantime you will not be able to exercise the privileges of your MECIR while it is expired. If you do not need to use it currently, then by all means defer it until a time when you need to activate it for use again - I presume that is what you mean by extending it.