I don't know the specific answers, but I can talk about it.
Currently, all the kingdom governments are supposed to be monarchies. In monarchies, the monarch is responsible for both legislative and executive powers. So, to ask whether any of the above things are possible, is equivalent to asking whether a monarch can do it.
Where two or more kingdoms are involved, all the monarchs involved have to agree on the actions. Moreover, other monarchs not directly involved may see their interests threatened and choose to object. Because no monarch is legally subject to the actions or decisions of another (i.e., they are sovereign), any action by a monarch that is not in the interests of another monarch is a potential casus belli. Whether any such actions in the game can result in a legal casus belli depends upon how the SBS, via the Soulbound Engine, interprets what sovereignty means.
So, I think it may be possible for kingdoms to form federations, merge (join together), and swap territories. Once merged, I don't think kingdoms can split apart or dissolve at the monarch's will, but that is because it is unlikely to be in the monarch's interest to diminish his power or create another rival. Secession or ejection are similarly unlikely, for the same practical reason if not for a legal or game-mechanical reason.
The exception will be federations, because federation retains the political identity of those who federate, without removing the sovereignty of any of the partners. If this were not so, then there would be no difference between federation and merger. If the agreement to federate includes means of the federation's dissolution, then a federation can be dissolved according to those means, at the discretion of the monarchs so designated to execute the means. If the agreement to federate does not include the means to dissolve the federation, then dissolution will probably require a casus belli on the part of one of the monarchs, followed by a successful war.