PHost 4.0 includes a new TRN command, SendBack (62).

 +0     WORD    Receiver race
 +2     WORD    Record Type
 +4     WORD    Data Size
 +6   n BYTEs   Data

This will copy the specified data (including record type and data size) verbatim into your util.dat. The receiver race must currently be 0 or identical to the TRN file sender, both meaning that the data is being sent back to the sender. This feature may be expanded to allow you to send data to other players someday. The main use of this command is to allow clients to "store" their auxiliary files in the TRN, using file transfer records (type 34). PHost does not interpret the data in any way. The upper limit for the size is 32000.