What causes Transactional SQL Server Replication to need to be rebuilt/re-initialised
To answer the question, you would need to test how many rows your change will affect (an update to a column without a where clause, or adding a column will affect all rows). A reindex will not cause replication to be "rebuilt". Can you clarify what do you mean by "rebuilt" do you mean all rows are re-replicated? or do you mean you are forced to snapshot?

To know what is actually being replicated, you can use http://msdn.microsoft.com/en-us/library/ms186983.aspx