Hi,
Sorry but the search index is file based and built on Lucene.NET, it is not connected to the database and there is no way to trigger indexing from the database, or at least I have no suggestion of how to do that.
If you modify the mojoPortal source code or the mojoPortal tables I cannot provide support for any problems you may have in a modified version. I will say that just adding some columns "probably" won't cause problems if you named them with a different convention and did not modify any of the mojoPortal stored procedures.
You might consider just using google or bing for site search instead of the internal Lucene search engine if your site is public and crawled frequently. We have built in support for using either or both of those, only problem is they won't be able to crawl content protected by roles whereas our internal search index is able to index all content and filter it in results according to the user's roles.
Best,
Joe