Changing the Size of A screen at runtime

Is it possible to change the size of a screen , just before it is called, or to move it it after it has been called.

Bascally I'm using

CALL FUNCTION 'Z_SIM_TEST' starting new task 'PDF Spools'

to create a new screen asynchronously, in a new session, and want the user to be aware that the older session is still there?

Thanks.