Any general tips for how to change your calling when trying to get a hen to come in instead of calling at the toms?
The first thing you have to do is get that hen to respond to you. Do what she's doing and call over her calls. She won't like that. As she gets more demanding with her calls, respond the same. She'll get more and more riled and come looking for you. Doesn't work all the time but enough to try.
Your calling like a "hen" in the spring so she will or she won't come to your calling. I have gobbled hens in more in the spring.
It can work at times if the hen(s) desire the company of another hen. Sometimes they do, but many times they will not want any company depending on how far along they are in the breeding/nesting process. Many times they will take the gobbler away from any competition. Being aggressive with the boss hen can work but she may not accept your challenge and may lead the gobbler away from your area. Sometimes you may call in one of the hens but the gobbler may hang back out of sight with other hens. You may just catch a gobbler at the right time that is getting a little tired of his hen(s) and call him up with the hen in tow.
Every situation is different, no absolutes here.
Calling hens is just another tool to get the gobbler in. It has worked for me several times and usually later in the morning. Like others have already said, answer a hen with just a little bit more intensity and emotion. I once called in a whole flock from about 300 yards away in a picked corn field from something I "said" when answering a hen in that flock. She lead about a dozen birds directly to me, even flying across a creek. When I shot the lead gobbler, the other toms started flogging him, walked off, then returned to give him some more. It was an exciting and interesting exhibition of the peck order.