I really seem to missing the point here... Why?
In general, you shouldn't have to permanently disable Windows Defender. If you choose to use a different AV, it's installer will disable Windows Defender (and re-enable Defender upon uninstall). And if it's a machine set up for some special purpose (maybe where maximum performance is needed), and doesn't need AV (maybe it's totally offline), just disabling Windows Defender's real time protection should be sufficient.
I can't think of any common scenario where Windows Defender really needs to be disabled, but I'm sure there are some niche reasons.
Edit: I see from Spartan's answer that other AV solutions may not totally disable all Windows Defender services. That's something I've never checked closely. Good to know.
Related story...
Once, I had a weird issue where Windows Defender started quarantining a script that I had written and used many times before. The same script was fine on all other computers using the same version of Windows and Windows Defender definitions. I should have just done a
Windows repair install, but I thought it would be interesting to see if I could completely remove and reinstall Windows Defender. I used
this removal tool which totally removed Windows Defender. But it was so well removed, I couldn't reinstall it. Doh! I then did the Windows repair install which brought back Defender, but it failed to start up. Doh! again. A second Windows repair install got everything back to normal and the issue with the script was gone.