[follow up edited from support email]
I tried the update with var(subj), which works fine while the program is running. However, I noticed an unexpected problem. When the session ends - directrt creates a new input file that is a replication of the original file and is named as the original file with the addition of a suffix corresponding to the value of var(subj). For example, the name of my DirectRT input file is primeprog. I ran a session with subject id = 555. Within the session directrt correctly displays 555 when I use var(subj). However, it subsequently lists in the "Select and run an input file" pull down the original file "primeprog" and a new file "primeprog_555" This also happens with other id numbers.