The DFSORT job I gave you does that assuming the UDL field starts in position 48 (as shown in your attachment). Does it?
It appears that what you really want is to replace 'UDLbbxxx' in positions 48-55 with 'xxxbbbbb' (b for blank).
Is that what you want? If not, what exactly do you want? Where does the UDL field start? How long is it?
Also, what is the RECFM and LRECL of the input file?
Did you try running the job I gave you? What results did you get? I can only guess at your input and output since you seem to be unwilling to use ubb code tags to show what they really look like, and/or give the position/length of the field.