The Jimenez Arms JA-380 is the latest reincarnation of the J-380 that was produced by Jennings Arms and Bryco Arms. The JA-380 is one of the most popular little handguns in history. Some call it a "Saturday Night Special" (See: Saturday Night Specials), even so, it can be a very useful and reliable handgun.
Customization is so far limited to individual users. However, if you check the links below "Taming the Jimenez JA-380", you will see that the author has created a website that deals with his experiences at improving performance and some minor customizations.