Texinfo provides several ways to define new commands (in all cases, it’s not recommended to try redefining existing commands):
Incidentally, these macros have nothing to do with the
command, which is for documenting macros in the subject area of the
manual (see The Template for a Definition).
Most generally of all (not just for defining new commands), it is
possible to invoke any external macro processor and have Texinfo
#line directives for error reporting.
If you want to do simple text substitution,
@value is the simplest approach (see Flags:
@clear, conditionals, and