@MrKim an
idea is to make your First Installation Exe file as package standalone build (but will only a launcher for you main jar)... as you probably do (i mean by pressing build standalone package)... and from it (1st extracting openjava) (and then) launching the main project as jar (with jshell and args need)... Also in the first-exe you can check for any updates at your site-ftp...
* But ofcourse that doesnt make it smaller... but at least can be one file that can be replaced.... easily...
* Also check that (an old thread):
Hi there... [Here the solution found !!!] creating a standalone exe with b4jpackager can be a big file... sometimes is little difficult to include in small size usb-sticks or want to have a progressive download bar that will not using internet download manager for many reasons... Check for...
www.b4x.com