help. valve spring install

Okay, im installing a set of crower dual valve springs on my LS b18b motor and i need to take my stock ones out. How do i do it without taking the head off. the heads gonna stay in the car. I have the the valve spring compressor, but my main issue is with the valve's. once i pull the stock springs out, the valves might drop into the cylinder.
how do i go about take n out the springs while keep n the head on?

you put whatever cylinder your doing at tdc so the piston is at the very top so the valve wont drop in

i was think n that too. if i put cylinder #1 at TDC, i will change both cylinder 1 and 4 springs at the same time. but the valves wont drop all the way down right if it's at TDC?

i normally just pull off the head.

i hear some people stick down nylon rope when they want to crack the crank pulley, if you do the same thing and fill up hte combustion chamber then there will be no room for the valve to drop, with the pistons at tdc and the nylon rope filling the chamber you wouldnt have to worry at all.