Question: When was anyone ever appointed to the position of an elder?
Titus 1:5 ¶For this cause left I thee in Crete, that thou shouldest set in order the things that are wanting, and ordain elders in every city, as I had appointed thee:
It has been my contention for a long time that Peter and the rest acted irrationally and impetuously in Acts 1. They had yet to receive the Holy Spirit, and so were acting on their own. Jesus told them to wait, but they didn’t. Jesus already had an apostle in mind with Paul, but Peter thought he HAD to do something.
Just what Christ loves, Christians arguing about Scripture.
The point is that once Matthias is an apostle, he is fully an apostle. So, we know that the apostles can appoint replacement apostles. And since a replacement apostle is fully apostles, he could then do anything an original apostle could do... including taking part in appointing a replacement apostle.