Here is my two cents.
1) Strategic capital move.
-people can somewhat bull!@#$ their way and pretend they are doing it for historic reasons before a couple months before a major war.
-to prevent stuff like this, you can provide incentives or disincentives of having a capital in somewhere. To be honest having a capital in the center of your realm probably makes more sense.
-also historically, countries did move their capital around to shorten their frontline. Of course no country moved it right next to the frontline but some countries did move their capital few hundred kilometers to closer for various - not just for shortening the frontline - reasons.
-can provide incentives to move capitals more frequently. Maybe having the capital in the same region for longer than 1 RL time when you can have your capital elsewhere can cause corruption that builds up overtime?
-Allow realms to put a capital in a non-city region. Don't need to change the region type. Just allow them to build Lv5 walls maybe. Maybe put a little crown mark on dynamic map or something.
Realm Merger:
-Should probably be allowed. When small realms merge to form a bigger realm, think of castile and aragon.
-When a small realm and a big realm merge, think of it as the small realm becoming a duke of a larger kingdom. Big countries did forcefully vassalize a smaller country historically. There were cases where a smaller dying kingdom eventually surrendered due to their incapability to maintain their country due to civil wars or other disasters.
-There just aren't enough incentives to merge for two large realms to form an even bigger realm due to various penalties so I doubt you need to worry about that too much. In most cases, I am guessing smaller realms will try to form a bigger one which should be fine since small realms these days are miserably small in many cases. Not much you can do with less than 10 people honestly.
-For now at least, you should probably be encouraging larger realms. Too many smaller realms don't really work. Some people think 10 realms with 10 people each will be ideal but it is not. Half of those realms will die or become too boring. It is heathier to have 5 realms with 20 nobles each instead. I think there is a critical number of people you need in a realm to make it work since it is very hard to talk to your neighbours in this game unless you travel or be in the same guild. If joining a guild was easier maybe that would help people communicate better.
