There needs to be a feature for splitting of the right hand side blocks at Special:PageMigration. This could be accomplished in following ways -
- Allow an option to add a new unit somewhere in between and perform manual splitting
- Perform the split on some text selection event and add a new unit after the current one in the DOM.
- Select the text to be retained in the current block and click the split icon. A new unit with the remaining text would be added after the current block.
Looks like 3 is a mixture of 1 and 2 and should be easy to implement. Comments welcomed.