[kbs666]

There isn't an automatic way to do this and it probably would be pretty undesirable if there was. You can manually copy snippets/sections from one topic to the other, delete the topic you don't want and scan the realm for new links.

If you really want this to work you either need to only have one realm where you input all the books on Golarion or create a top level realm with all the topics the books will produce and import that skeleton realm into empty realms to do your data entry before merging them back together.