The following is the documentation on Lodestone in Configuration Commands for the /crosshotbar, /chotbar text command.

Subcommands
set "action name" [number] [slot name] - Set the specified action to [slot name] in cross hotbar [number]. If [slot name] is omitted, the action will be set to the slot with the lowest available number. If both [number] and [slot name] are omitted, the action will be set to the slot with the lowest number available on the cross hotbar with the lowest number available.
Not all actions work using this syntax. Either the documentation is inaccurate, or the text command is not working in all situations. Specifically, pet actions cannot be set using the above syntax. It would be nice if the syntax worked for all actions like the documentation implies, or in lieu of that, the documentation was accurate to which actions are excluded from this syntax.