not a big thing
pull old push rod out, make sure not to damage the sealing at the booster.
Get the new one in. Key is now the "small" gap needed between the push rod top and the master. Here you have to play a bit..master in and out. There is a spec for the gap I do not have at hand, but it is very little. (1 millimeter) You need a trick to measure the gap with master in, like put some paint on the tip and see if it binds.. Adjust the tip screw accordingly.
Key is at the end to get the seal in place correctly as you otherwise get no stable vacuum!