A: For assigning a 
value to (a parent process's) environment value
you have to access and manipulate the Program Segment Prefix 
andMemory Control Blocks. This is a rather complicated undertaking. 
Asource code with an accompanying article by Trudy Neuhaus can 
befound in PC Magazine Volume 11 Number 1 pages 425-427.
   The budding TP programmers should note that the elementary 
trickof Exec (GetEnv('comspec'), '/c set key=whatever') will achieve 
onlya transient result for the duration of the exec shell. When you exit
the shell after this endeavor, the environment will be as it was.
   Here is about the why. When the above command is executed, 
MS-DOSmakes a copy of the environment, and uses the copy. When the 
aboveshelling terminates, the copy of the environment is deleted, and 
theoriginal is restored. Hence the above trick cannot be used to 
changethe parent environment.   If you don't want to try to go through this rather complicated
task yourself, the routines "SETEVN   Set a parent environment variable 
(variable=value)" "SETENVSH Set an environment variable for the duration of 
shelling"can be found in my TP TPU collection ftp://garbo.uwasa.fi/pc/ts/
tspa34*.zip (* = 40,50,55,60,70). No source code is included, nor
available, though. From zeta@tcscs.com Gregory Youngblood: 
Fora source code see /pc/source/setenv.zoo at Garbo.
   One further detail. Users sometimes ask how one can change 
theprompt or the path from within a Turbo Pascal program. This is in 
noway different from changing the value of any other environment
variable. Both PATH and PROMPT are environment variables 
that can beset with the MS-DOS SET command in the fashion described in 
theabove. This is not changed in any way by the fact that you can 
applyPROMPT and PATH also in an alternative format not requiring the 
SETcommand.