Illustrator will always keep the document color mode. If you want to convert it, you will have to make Illustrator do it.
1 person found this helpful
Are you sending native Ai files to the print shop, or PDF?
One problem with converting RGB to CMYK in Illustrator is that RGB black will usually convert to rich black, rather than black only. An action or script may then be required to select specific rich black values and convert them to K only.
PDF colour conversion may be a better option using Acrobat Pro, it can greatly simplify the process of cleanly converting RGB black to K only.
I would always keep a copy of the original client Ai data, then make a working Ai copy and make changes as nenessary. Then a separate output PDF file may be created from the working file (so at least 3 files).