How do I install a specific version of a package?

I'm on Manjaro, and accidentally upgraded my D compilers to those that have the AI slop contributions. I uninstalled them from Pacman, I wonder if I can do it via Pacman, or have to do it manually (LDC has a (very) temporary install script, meaning it tricks the terminal session into believing it's the reference compiler DMD, which is not ideal, want a permanent solution, as this one conflicts with GUI editors and the package manager).