MathLive input in obsidian editor mode.

Edit the equation in mathlive block below the latex display block.
It is also possible to assign a hotkey to toggle the display of mathlive block.
When the MathLive macros setting is set, the new command is available in MathLive widgets but not in builtin mathjax block due to some designs of mathjax.
If you want the new command to also show up in builtin mathjax block, you can use the copy button in MathLive macros to copy latex \newcommand command, then paste it in mathjax block in every page or use a plugin to preload those new commands.