How to use the "user paramter"?

[Chen, Song]

Hello, all
  I add a "user paramter" in my thread, name "prodid", and valued 
"${_StringFromFile(prodid.txt)}"

  And then in one of my "Http Request", I used it as ${prodid}, it worked OK. 
Each time it read one line and give the value.

  But now my requirement is in each run, there need 2 Http Request, each will 
use ${prodid}, and they should be different value, that is, should read 
different lines, but now it seems it all use the same.

  How to deal with this?

Thanks

Chen Song