I can use solrnet to do crud to the index. Afaik, solrnet depend on init which specify schema of each connection. The question is, can I mergeindex using solrnet? is solrnet support it? I want to control my index from the application that makes solrnet have behavior like secondary index.
No, SolrNet does not currently support the Multi-Core commands, please see issue #8 on the SolrNet issues list.
According to the last entry in the issue, this support was started on a fork of the SolrNet source in GitHub. You might consider looking into what has already been started and perhaps completing the functionality and contributing it back to the project.