Problem 1: Multiple Blogs need to be merged into a single one.
Problem 2: One or more Blogs need to be moved into a Community
Solution with Websphere Commandline Interface
HCL Connections does not provide any tools for moving / merging / copying Blogs. You need to write your own code that either modifies the relevant tables of the BLOGS database directly, or which uses the REST API to create the new Blog.
Solution with Connections Administration Toolkit (CAT)
Navigate to Content And Access – Blogs. There, you can create a list which contains all Blogs that are part of the merge / copy operation.