Pre-fill Content Editor Fields

The “filename” field for one of our content editors follows the format “mwMMDDyy”, where “mw” is a literal string, and MMDDyy is a date transformation of the current date. Currently our users enter this value manually, but i wanted to try and automate it. I was able to get the second part of the filename using “sys_DateFormat(MMDDyy, PSXSingleHtmlParameter/sec_currentdatetime, )”. However, I am unable to append the “mw” value before it. i tried using “sys_concat”, but it only seems to allow literal strings and not user defined functions. Any thoughts on how i can merge these two fields?

Thanks
Raj