Jang,

SET SAFETY setting is scoped to current datasession. I assume your report has a private session which has SET SAFETY ON by default.
As far as select how many pages to print, you may try:
repo form myreport to print for _pageno<=lnUser_Enter_Pagenum
where lnUser_Enter_Pagenum is the number from the spinner setting chosen
by the user.
The above code is written roughly, and has not been tested.

P.S. They really killed a lot of chicken lately. I am from H.K. too.

Kam.