As I re-read my responses, I realized that I could have done a little more to explain this, so here goes:
TMP and TEMP are simply variables. These are special variables that are available system-wide, not just within the context of a single command prompt or batch file and are known as "environment variables".
Suppose now that some program wants to save something to your TEMPorary location. That program can simply check to see what TEMP is set to obtain that location.
If we change the location of the TEMP variable within a batch file, for example, by using the command "set TEMP=T:\Temp", then if something in your batch files checks to see what TEMP is set to, it will be handed the value that you set, in this example, T:\Temp. As was noted earlier, this affects only that instance of the batch file. If you end the batch file and then open a new command prompt or run a new batch file, that new batch file will inherit the value from the environment variables. Put another way, it will see TEMP as being equal to what is set in the Environment Variables.
Bear in mind that all this assumes that whatever you are running actually checks to see what TEMP (or TMP) is set to. If your batch file does not check this, this this whole discussion is moot.
Please do let me know if you need any further help!