If you need to replace the value of a field you need to create a new field in a derived view. An example of the code giving you the result in your question would be as follows (xxxx is the viewname.fieldname you want to replace)
CONCAT(SUBSTRING(xxxx,0,1),' * ', SUBSTRING(xxxx FROM LEN(RTRIM(xxxx)) FOR 1))
This assumes the field is text and has trailing spaces and is variable length.
Remember you can also use functions like GETSESSION so the replacement only occurs for certain conditions. ie only apply this mask to user 'Dave'.
CASE WHEN (getsession('user') = 'Dave') THEN (CONCAT(SUBSTRING(xxxx,0,1),' * ', SUBSTRING(xxxx FROM LEN(RTRIM(xxxx)) FOR 1))) ELSE xxxx END
Hope this helps.