Not sure if there are any date formats in ash, as I'm not really an ash programmer. There is a Mafia command string format_date_time( string inFormat , string dtg , string outFormat ) which translates one date format to another though.
The current format is a standard format which allows string comparisons to make sense whilst also allowing a human to read them.
I'm really not sure what you're asking for other than that you want the preference to be different ?
Edit, I'll grant you that YYYYMMDD as used in the linked thread is slightly more standard, but only when used by code, you wouldn't use it where humans were going to read it.
Edit2, if you want that format, just use umdDate = format_date_time( "yyyy-MM-dd", getProperty( "umdLastObtained"), "yyyyMMdd" )