Yes. You can specify your favorite macros and add your favorite packages (this is a list of LaTeX packages we support)

Macros and packages are defined in a file called header.tex

In Authorea Standard, you have to navigate to the Data folder and create the file yourself. In Authorea Beta, you can click on the Edit Macros in the toolbar, under Settings ⚙

and then go back to your article and write in a LaTeX block Hello $\msun$, you will generate “Hello M⊙”.