If the hair is packed tight and you have a nice dense body and you tie them on after you trim the hair, they will leave the hair separated all the way around the body. if you tie them on between bunches of spun hair, you wont have this problem. With rubber legs, they will stretch out of the way. you just have to be careful if you're trimming with a razor blade.

I've also seen then threaded straight thru with a bobbin threader, but unless you can get under a thread wrap, they will put straight out.

I tie them in during the spinning. I don't have a problem trimming around them, I have a problem REMEMBERING to add during the spinning!!! When i HAVE to add them after wards, I cut in have (left & right), use a drop of SA glue to hold the (body side) tips together, then use Shoe Goo to adhere down in the trimmed hair. Use a half hitch tool to push aside the hair and make a 'socket' for the legs. One dried, they will not come out without ripping a chunk of hair out with it.