Ballsign mod is, simply put, created by double-capping a Sakura Ballsign or Gellyroll and adding Super Grip and Dr. Grip grips. It’s a personal favourite, and originally created by Bonkura. If you decide to mod it, don’t be surprised by how short it is. It’s about 16.5 Cm, wich I must admit is very short, but you get used to it.
You need 2 pens, since the mod requires a cap on both sides. Remove the refill, the clips sticking out from the pen caps and the back plug. Now put in whatever insert you feel like, recap on both sides, add about 1.5 Cm Super Grip grip (The Dr. Grip grip will slip of if you don’t have this) and a bit more than 0.5 Cm Dr. Grip grip over that, and voila! You’ve made yourself a Ballsign Mod.