Booking reward seats

Hello there, just looking for some more V-flyer expertise please!
I am trying to book a reward flight for a friend using my miles and PE upgrade vouchers.
At the minute there are no PE reward seats in either outbound or inbound in the 2month period I am looking at-Mid August to mid October (although there are loads of UC!!! Wish I had the extra miles required!!)
So my questions are:
1 -can you pay to select extra leg room seats on an economy reward seat?
2-if I did the above and then PE became available, can I still use my PE credit card vouchers to upgrade the original redemption? Would the seat selection payment be refunded?
Thanks, Jo

I have done this
Booked E
paid extra for legroom
when PE became available
used PE voucher
got refunded for legroom seat.

If in doubt, phone the Call centre for confirmation

Thank you, I hoped it was possible!