Default [Q] Go sms appellation in group texts: how to costomize it?

Dear all,

i send group text to a bunch of people and I noticed that now Go sms asks me if I want to add an appellation to the text. Basically it takes the name from the phone book and he puts it at the beginning of the text, so the text looks like:

APPELLATION, wanna play soccer tomorrow at 9 pm?

I tried it with my friends but it does not take only the first name, but also the last name, and most of my names in the phone book are like Mick Boston, Andrea Beer Pong and stuff like that, so my friends receive texts like:

Mick Boston, wanna play soccer tomorrow at 9 pm?

Andrea Beer Pong, wanna play soccer tomorrow at 9 pm?

Do you guys have experience with this? It says click on the appellation to modify it but after clicking on it I cannot modify it. I went on the app options and I cannot find anything. I would like to have the option to choose "Use only first name as appellation", so all the other stuff that I write in the last name area (also if its a standard last name) does not appear. Even if i d replace everything with the real last name, who would ever invite people using first and last name?
thanks
Cheers
A.