This has been on my to-do list for some time, ie. allowing users to update their servers list (by automatically downloading the latest version from the mIRC website) while keeping their favourite servers. It's tricky to implement in a way that will work for most (and especially non-technical) users.
Displaying a merge dialog that highlights differences between the old and new servers.ini and allows users to shift servers back and forth, deciding which to keep or update - this seems too complicated and time-consuming.
Allowing users to mark some servers as read-only sounds good. However it would depend on users pro-actively marking servers that they know they will want to keep in the future. If a user does not do that, and I suspect most non-technical users will not, then it does not help.
Another option would be to look at the [recent] and [success] sections in servers.ini during the update. These are currently limited to 20 servers for each section which could be sufficient to ensure a user's most recent or favourite servers are retained. This would not need any user interaction. Unfortunately, this option would not work if a user regularly uses the "Clear History" feature.
