If an ABAP program has following syntax:

   CALL TRANSACTION 'VA02' AND SKIP FIRST SCREEN.

it seems that GuiXT Script for first VA02-screen (SAPMV45A.E0101) is bypassed. Is that correct?

If the first screen is skipped it cannot be processed by GuiXT, since it is never sent to the frontend. If you need to initialize variables in your script, the system variable V[_transactionid] is a possible alternative. Example:

if not V[va02_transactionid=&V[_transactionid]]

  Set V[va02_*] ""

  Set V[v02_transactionid] "&V[_transactionid]"

endif