I need to change some biomes on my Minecraft server, but I'm on Ubuntu and all the biome editors I can find are for Windows. How can I edit the biomes of my world on Linux/Ubuntu?
Just install WorldEdit, which will work cross-platform, and modify biomes in-game with the biome brush.
If you have time, disk space, a Windows iso, and a powerful enough computer, you can try to run Windows in a virtual machine, like Virtual Box. This tutorial explains how to setup what the community calls a VM (Virtual Machine). Don't forget to read the description!