The CSA simply will not have the resources to take territory from a European power (even Denmark), and Mexico with Maximillian in charge and French support, not happening. However if you get a successful filibuster in one of the Central American little countries, or even one "mostly successful", you might get the filibuster leader appealing to the CSA for annexation (like Hawaii/USA OTL) which might not be smiled upon but most likely would not cause the USA or UK (or anyone else) to do anything. A "back door" expansion like this is all you might see, no matter how much various CSA leaders might want differently. If butterflies somehow caused a major fragmentation of Mexico, you might see some territory tasken but very unlikely.
Why would the U.S. go along with Confederate designs on Latin America, particularly ones which would give Dixie Pacific Ocean access?