Yes, it is possible, but not certain if it would be female already and fight w/ your existing.
What size is new guy?
You could get really lucky and they might pair up, if it's small enough to still be a he.
You have just one clown now, correct?
Yes, they certainly can.
The safest way to intro is in a specimen container, you should be able to tell if your existing darts at it like it wants to kill it, or just curious, and sometimes we float in container for a couple/few days.
Your tank going by sig seems established, as long as big enough and lights are decent I see no reason to not try.
BTAs like to have their foot planted in a hole of a rock. To simulate this some people will use a piece of PVC. If you find a size that is appropriate for the foot you can set the anemones foot on top of the opening (and in some cases gently help it into the tube). Once in, you can place it in your tank and cover the pvc with something.