Yes with Visual CUT like Brett said. It has a specific function for _Excel Export as Tabs in Existing / New Spreadhsheets_. Also has it's own ODBC Export which extends the regular Crystal ODBC export (if that's what you're intending) to allow appending to a table, which could be Access, SQL, prolly Excel too if you define a named range).
It's smaller cousin called CUT Light, the DLL added for Crystal which lets you see additional functions in the formula editor is more limited I believe. There is a FileAddText() function to allow appending text to an existing file, which for example, if formatted for the columns you want to export can add rows of CSV output to an existing CSV. Visual CUT is better for this purpose I think.
Does this sound right @KevinMoyes and @JimWoodhead